Hi, and welcome to the forums.
Yes, Time Machine can restore individual items, including apps. Here's a demo:
Time Machine Tutorial
Time Machine can also be used to restore all your configuration, settings, apps, users, preferences, data, etc., after purchasing a new Mac, or doing an Erase and Install. See the *Erase, Install, & Migrate* section of the
Glenn Carter - Restoring Your Entire System / Time Machine *User Tip* at the top of this forum.
And, if your hard drive fails, it can be used to restore your entire system to the exact state it was in at the time of any backup. See the *Restore System From Backup...* section of that same Tip.
But you may want to re-think your strategy. It's usually much better to delete what you
don't want, rather than, in effect, delete everything and try to pick and choose to restore what you
do want.
If you're thinking of the Windoze world, where a PC will gradually slow down, and needs a periodic reinstall to clear out assorted junk and speed it back up, that's rarely the case with OSX.
While we don't know what the Snow Leopard procedure will be, usually when Apple releases a new version of OSX, all you have to do is an "Archive and Install, preserving users and settings." That moves the current OSX into a "Previous System" folder, which you can delete as soon as you're comfortable, and leaves your configuration, settings, users, etc. alone.
Perhaps if you tell us just what you're hoping to accomplish, we can provide better advice.
