CCleaner is very good program for keeping your computer running fast. It fixes registry and cleans unwanted files. It can be obtained here
Registry Cleaner also works well for this.
Another thing is viruses. Vista is very secure but you always need to be conscience of what your downloading. Websites that have Keygens, Cracks, or Serials
are usually dangerous. I recommend AVG
because it is the best. It finds all the kinds of Viruses. Most hackers are trying to break in through Norton because many people have it. It also comes on most computers. I reccomend buying AVG because the freeware version finds things but is not always able to clean them. Also, even though AVG gets spyware, I like Spyware Doctor
just in case. The freeware version of spyware doctor is here
Defragmenting every now and then isn't a bad idea. Also, disk clean up helps. These can help you if you have limited disk space as CCleaner does.
Last but not least, always update your computer. This will patch problems and improve your security.