OnyX lets you easily change the format and default location of your screenshots.
The Geeky Way: Open Terminal (/Applications/Utilities), type in the following: defaults write com.apple.screencapture type -string TIFF and then hit the Return key. Now log out (Apple menu > Log Out username) and log back in. Henceforth, your screenshots will come out as TIFF files. Use JPEG, PDF, BMP, or PICT in place of TIFF if desired.
The Easy Way: Download OnyX (free, www.titanium.free.fr/pgs/english.html), Cocktail ($14.95, www.maintain.se/cocktail), or TinkerTool (free, www.bresink.de/osx/TinkerTool.html) - each of these powerful utilities provides a simple pull-down menu for changing the default screenshot format.
