Use IDE for backup, use SATA for windows and all games.
Used to run off an IDE, upgraded to a SATA, and previous windows XP installs used to take an hour or so to copy files, but the first install with the SATA (Sata 1.5, not even 3.0GB!) and it took somewhere around 15 minutes or less to copy all files!
Windows, Windows swap file, windows temp files, game executables, skins, textures, loading files into memory, all of these are required for smooth gameplay. They will all be faster on the SATA, most cases. Especially if the IDE is an older drive (already has some miles on it).