Ah the impossible to uninstall problem. Usually this happens when you delete a game from your program files or wherever it was but it still shows up in the add/remove list, so when you go to uninstall you get crap errors and nothing happens.
Most games have their own file used to uninstall. When you delete the folder the uninstall file was in, the uninstall file is lost. Yet the settings in registry, and/or saved games in my documents or accessory files elsewhere remain which usually causes the slowdown. To fix this just reinstall the game and uninstall. If this doesn't work (sometimes it hasn't for me) you have to either edit the registry by hand or do searches for all key files that might be hidden somewhere. Or you can just remove the program from your add/remove list and forget about it which I've also done in the past without many problems, usually because I format my operating system every other year or so I don't get any major long term problems.