Get RegCleaner from
http://www.jv16.org/ . Its an amazing program. I use all the time at work & home. I've yet to see it mess up a regisrty on any machine. I've used it on Windows 95, 98, ME, XP, 2000 Pro, 2000 Advanced Server, NT 4.0 Terminal Server, NT 4.0 Server.
Try that. Then goto
http://windowupdate.microsoft.com and get the latest updates, especially Internet Explorer 5.5 if you don't have it.