Here's a brief tutorial (assuming Windows XP):

1) Cut a hole in the box... He Heh - just kidding! I kid, I'm a kidder! Seriously, hit <Print Screen> while in game - this saves the picture to the Windows clipboard

2) Alt+Tab out of game, click <Start>|Run

3) Type in mspaint and hit the Enter key (launches MS Paint - if you prefer another application, please launch that instead - I use either MSPaint or Gimp depending on what I want to do)

4) Hit Ctrl+V to paste in the picture from the clipboard

5) Edit the image if you wish

6) Save to whatever format you wish (typically .jpg or .bmp)

7) Upload the image file to some image hosting website (or your own website if you have one, but if you did then you probably already know how to do all this . Personally, I use a free Photobucket account in conjunction with the Flock (Firefox-based) browser for Photobucket. Here's a link if you're interested (linky...)

8) When creating your post in the boards be sure to use the URL UBB Code, not the Image code. URL works, Image doesn't. Btw, most of the websites will have a variety of links ready for you to cut and paste. If you're using the URL code, select the direct link. Here's an example:

Picture Link Example

It's also important to note that you should post a direct link to the picture itself, not just the page in which the picture is stored. Here's an example:

Do this: Unique Armor - Female

Not this: example of what not to do

Why does it matter? Notice the ads in the "what not to do" post? Depending on the host you use, sometimes those ads are NSFW (Not safe for work) or are inappropriate for minors (*cough* Imageshack *cough*). If you post something that has objectionable content or links to such, you can punished because it violates the rules. Be considerate and post a link to the picture itself.

Also, while you can just paste a link directly into the post, it looks ugly and doesn't let you add a description. Here's an example:

http://i201.photobucket.com/albums/aa64/ripper_mcgee/Dungeon%20Runners/LiluLook2.jpg

Vs.

Unique Armor - Female

I hope this helps! Have fun!