Please see the most recent updates in the "Where did the .com name go?" thread. Posts number 16 and 17.
Works the same in windows 7 also,thats what I use,it works good.I've been using 'Snapper' for a while now and quite like it.
http://www.michielovertoom.com/software/snapper/
Don't forget that FSX has it's own inbuilt screenshot tool too. Hit the 'V' key in flight and the screenshot is saved to your 'My Documents\My Pictures\Flight Simulator X Files' folder (in XP at least). The file is saved as a .bmp (better quality) and then you can open it in any photo editor and resave as .jpg if required.