Control and F11 will take screenshots and put them in your SH folder, but they are .BMP files and so they might be better converted to .JPEGs, most file hosting sites prefer .JPEGs, as they are compressed more (with some loss of quality but nothing major).
FRAPS will also take screengrabs (you can choose a folder where you want it to save them).
Using the PRINT SCREEN key on your extended keyboard will also place a screengrab in your system memory, if you do this and then open a photo editing program (such as Photoshop), you can then hit Control N, Return, then Control V and this will automatically create a document at the correct size and paste the screengrab from your memory into the new document. Using this method, you'll have to flatten the file in most picture editing programs to save it in a lot of formats however, as not many support layers other than .TIFF and .PSD.
Oh, and the Delete key on the numeric keypad hides the interface.
Useful info about various picture file formats can be found here:
http://en.wikipedia.org/wiki/Graphics_file_format
Have fun.
Chock