In windows 2k, and probably others, using CRTL/Print Scr will capture the screen. Alt/Print Scr will capture the active window, e. g. just the active excell spreadsheet. Then paste into another program, e. g. Word, paint, etc. , save as a jpeg, and upload.
Oh, by the way, windows=yuk!, Linux=yeh! Couldn't help myself. :-laf