hey Jinny,
If you do a system restore, you should not loose anything.
First off I would run the antivirus and a spyware program to make sure that all is ok in that respect. If you have a system registry cleaner, I would run that as well then do a defrag. If things are still not working right, then do a system restore to a day when you know that the computer was running properly.
Vista is a huge program. If you put Vista on a computer that does not have enough memory, it can slow it down tremendously. I would also check to see what programs are running at start up. If you have a lot of programs starting up such as IM programs, windows messenger, aol messenger, msn messenger etc, will also slow your computer down. I find no need to start these until I want to use them.
erdfg
(sorry, that was Amy being a turd) LOL
Hope that helps!

sabby