I'm not sure if this is a global issue with excel, but it's happening on all the computers here (Excel 2002, XP SP2)
If you select a cell, and go Ctrl-V when there's a screenshot in the clipboard, the image gets placed in the cell you've selected.
However, if you're got a copy/paste of something say from MS Paint, or any other image, if you do the same thing, the image goes directly to the top of the sheet.
Any ideas why this happens?