Question: What do you do when add/remove doesn't work beacuse you are missing the uninstall file, and it is other wise corrupt?
Answer: Try installing it over itself. That should recreate the uninstall file so that you can then uninstall it.
If you don't have the install files to be able to install it again to fix the error in the uninstall then the only other option is to manually clean up the system - delete all of the files you know belong to that application and then use a utility program to attempt to clean the registry. Unfortunately you will not be able to clean everything out in that instance unless you are very lucky. What is left behind probably wont hurt your system, it will just waste space.
This article written by Stephen Chapman, Felgall Pty Ltd.