After you take the screenshot in sof, goto your soldier of fortune double helix mp test/demo/mp/screenshot folder. It should be in there.
If you have vista, and your soldier of fortune folder is inside "program files (x86)" then it might or might not show a "screenshot" folder. Vista puts some things in weird places, and I don't know where lol.
As for posting, I upload my photos to photobucket then they give you the code for posting on the forums too.