If you know what your doing you can go to the Registry Editor and check under HKey Local Machine>Software and note the name of the softwares you once had but that the names are still there. Then start a search at your My Computer and search for those names you noted, you should even find other key names you know were removed.
But to make it simpler go to www.zdnet.com
and download jv16. It is a small program that will do a great job at removing all unnecessary keys in your registry.>>All make sure to create a restore point before starting.