Roadkill this is what I wrote about screenshots in the "How does one PBM?" sticky:

Quote Originally Posted by econ21
(1) I use FRAPS to take screenshots. FRAPS is a free programme you can download from the web. RTWs screenshot function should work as well, but gives me all black TGAs. FRAPS is very easy to use: download & install it, then run it before each RTW game and during the game you can press F10 whenever you want a screenshot.

(2) Screenshots are saved in TGA format and are rather big. So I edit them with Irfranview to reduce them to 75% size and save them as JPG. Irfranview is a free programme you can download from the web. Many other packages would do as well.

(3) Finally, I upload the jpgs on

http://www.imageshack.us/

Once you've browsed to your jpg and clicked "host it", imageshack will take you to a list of various links you can copy into your post. I find the one they list as "hotlink for forums (2)" works fine, so just cut and paste that link into Org post and you are done.
It sounds intimidating, but you will soon get the hang of it.