Usually people buy newer products to upgrade or update their computers. In the case of Vista though, buyers have been so horribly dissappointed that companies such as 4All Memory are coming up with updates which promise to take your computer from Vista to XP.
When you upgrade for Vista, you really need to do two things. First, you need to upgrade your computer memory. Second, you need to get rid of Vista and use XP again since it's faster, more stable, less of a system hog, and generally makes your computer much happier.
4Allmemory.com should be able to help you out in case you need any.