Turbo Tax uninstall, and Common Files

First off, what is the Common Files folder used for in XP? Can I delete that junk?

Second, I was watching screensavers this morning, and they were mentioning the newest version of Turbo Tax had spyware, and it wouldn't uninstall. Like that includes me. I don't need that, but after getting home from work, my sister was here, helping my dad on taxes, and guess what...she installed her version of TT on the computer. I'm sorry if I'm a bit crazy when it comes to computers, but I can't stand when something is out of place, and tend to keep things organized in certain folders. And shes just the opposite. Ok, so will Spybot get rid of that spyware thats in TT? And I wonder what all TT installs. I have loads of shortcuts that shoot over to Common Files folder, and several other files thats been "modified" on this date. I can't tell which ones were ones that were installed with TT. I want all traces of it, and other applications it put on the computer off the hdd. Any advice. (Of course, first I have to choose uninstall, but that never gets rid of everything)