Since there a many guys out there who still have problems creating skins or using others skins, I'll try to answer the most asked questions:
Q: How do I install a custom skin?
A: First of all, pick unpack your skin if necessary. Put those files (*.bmp and .xml) in a random folder. Call it whatever you want. I'll call it SKINA here. Put the folder SKINA in the folder named skin in the CycloDS folder which can be found on your microSD card. You might have to create the folder "skin" first. In the end, it should look like this: X:\CycloDS\skin\SKINA
If you want to add another skin, just follow the procedure once more and call the folder SKINB if you want to: X:\CycloDS\skin\SKINB
In the end, you can choose between your now installed skins in the CycloDS Evolution settings menu.
Q: How do I create a skin?
A: First of all, you need a better graphic editor than Paint *cough* - like Photoshop. If you don't have 500$, you can go with the best freeware app for PC:
GIMP.
Next you have to create the background for both screens. If you use the regular skin.xml file, you have to name the BG for the touchscreen bottom.bmp and the BG for the topscreen top.bmp. Simple, isn't it?
Info: Color transitions cant be displayed properly, because the Nintendo DS screens are limited to 16bit, this means you can't see as many colors on DS as on your computer!
If you want to use one picture for both screens, this information will help you to keep the proportions: the space between the two screens is around 90pixel!
Be sure both backgrounds have the dimensions of 256x192 pixel and saved as a 24bit bitmap(.bmp) or you'll get a black background!
Next the buttons on the touchscreen. The dimension should be 128x192 pixel. Each button is 64x64 large and is made out of two pictures: the selected(left) and the unselected(right). You can see which button is which in this picture:

Now you have to choose ONE color which should be transparent if you don't want to fill the whole space of 64x64 for each button. The most used one is magenta(#ff00ff), because it mainly doesn't show up in the visible graphic (use darkblue if you are going to do a Barbie skin

)
Fill all the space which should be invisible with this color! Remember, everything else than magenta will be visible(!), so you can't use anti aliasing for the edges

Also save this one as a 24bit bitmap(menu-icons.bmp).
The next part are the cheat-icons. If you do only want a skin for yourself and a good boy, you can skip this part

This part is nearly the same as the buttons. You have a 32x48 which is made of 6 different icons. The best thing I can do to teach you this part is showing a picture:

Hint: do not use larger dimensions for each icon - it won't look good!
Now the easiest part: the scrollbar.
The scrollbar is made out of two parts: the bar and where it scrolls

The picture is 8x64 pixels large. The first 48 pixels(y axis) are for the bar. the size of the bar is fixed on the CycloDS Evolution, no stretching!
The rest is for the rail. Use magenta as the transparent color as well, if you want to.
Heres also a picture which might help you:
Your skin is nearly finished, all you have to do is to edit the skin.xml file(use Notepad). Heres a example of the file:
Code:
<?xml version="1.0"?>
<skin>
<!-- Information -->
<skin-name>My new skin</skin-name> <!-- skin name -->
<skin-author>Max</skin-author> <!-- your (nick)name -->
<skin-version>1.0</skin-version> <!-- version of your skin -->
<!-- Bitmaps -->
<top-bitmap file="top.bmp"/> <!-- defines "top.bmp" as the background of the topscreen -->
<bottom-bitmap file="bottom.bmp"/> <!-- defines "bottom.bmp" as the background of the touchscreen -->
<menu-icon-bitmap file="menu-icons.bmp" transparent-colour="FF00FF"/> <!-- defines "menu-icons.bmp" as the main menu buttons. The transparent color is magenta(FF00FF) -->
<cheat-icon-bitmap file="cheat-icons.bmp" transparent-colour="FF00FF"/> <!-- defines "cheat-icons.bmp" as the cheat icons. The transparent color is magenta(FF00FF) -->
<scrollbar-bitmap file="scrollbar.bmp" transparent-colour="FF00FF"/> <!-- defines "scrollbar.bmp" as the scrollbar. The transparent color is magenta(FF00FF) -->
<!-- Colours -->
<window-fill colour="ffffff"/> <!-- This is the colour used to fill the dialog box windows -->
<button-fill colour="b2dfe3"/> <!-- This is the colour used to fill the selected button for the button dialog boxes (such as the cheat code prompt). -->
<window-border colour="00a9cc"/> <!-- This is the colour used as a border for dialog box windows and for the outline of buttons. -->
<text-list colour="000000"/> <!-- This is the colour used to draw text for the game list and cheat code list. This text is drawn over the middle area of the bottom screen bitmap. -->
<text-window colour="000000"/> <!-- This is the colour used to draw text for dialog box windows. This text is drawn over the "window-fill" colour. -->
<text-status colour="ffffff"/> <!-- This is the colour used to draw text for the status info such as the current working directory, time etc. It is drawn over the top and bottom "bars" in the bottom screen bitmap (ie: the first and last 16 vertical pixels). -->
<selection colour="98d4d9" transparency="7"/> <!-- The colour specified is used to draw the selection bar over the selected item in the game list, cheat code list or settings menu. The transparency value is used for blending the selection bar into the background. The range of this value is from 0-15; the higher the value the more transparent the selection bar will be. -->
</skin>
now put everything(top.bmp, bottom.bmp, menu-icons.bmp, cheat-icons.bmp, skin.xml) in a folder called skin. Put this folder on your microSD card in the CycloDS folder.
That's all you have to do. Your skin is finished!
Visit
this thread if you still have problems with creating a skin or want a free sample.
Q: The background(s) of my new skin is/are black! What can I do?
A: Please check if the dimensions of the related background are 256x192 pixel. Check if you saved it as a 24bit Windows Bitmap(.bmp) file called as in the skin.xml file(standard: bottom.bmp or top.bmp). Check if the bitmap is in the correct folder.
Q: My buttons/icons/scrollbar shows parts that should be invisible. What can I do?
A: Be sure you set the transparent color for the right parts in the skin.xml file correctly. Check if the color you choose to be transparent is the right one. Remember: anti aliasing is NOT possible!
Q: How can I snap a clean screenshot of my skin?
A: Theres a great tool by ste123:
Skin tester
You might have seen a thread about it but never wanted to click it, but now, you have to
Q: Where can I upload my skin?
A: First of all, you have to compress/archive them with the Windows or
7-zip. Then you can use the forum attachments:

You have to use the .zip format, .rar is not allowed, but 200KB should be more than enough