Good tip. More tedious than reinstalling, but faster and less tedious.
If the file can't be deleted because it's in use, then do this: Make a folder on the desktop called "Bad boys". When you find a file that's not supposed to be running, drag it to the bad boys folder. Then restart the computer. Now you will be able to delete the bad boys.
Slightly more tedious but worthwhile is this: Every time you discover a bad file, look for other files with the same exact creation date and time as that one. It's likely they'll be in the same folder or be similarly named. Trash them all, using the bad boys folder technique if you have to.