Regardless of what some say, Vista does not offer extra features or functionality beyond what XP already offers. There are still large numbers of people downgrading from Vista, back to XP. If you have XP and try running Vista on it, your computer and its applications will run a lot slower. If you use the same hardware that people say, "my system run good on Vista" for XP as I have, you will find that XP really flies. What many Vista users forget is they are comparing Vista using hardware that is literally 4 times stronger on a 5 year old computer. All it takes to run XP is 512 MB RAM. That means, if you use an application and have 2 GB RAM, 1.5 GB can go to you application. With Vista it's much less and your apps run slower.
Right now Vista gives XP users no reason to upgrade. XP can run the same software and more efficiently. Most who have XP are waiting for Windows 7 which is suppose to be Vista with all the bugs and platform issues worked out.
In my view,businesses are not upgrading to Vista for a reason. And since Windows 7 will come out in a year or so and your computer is running fine now, it's probably not worth the money. If you want to switch to Vista, all you have to do is ask yourself this question, what does the version of Vista have that XP doesn't have and have someone show you.
I have returned 3 Vista SP1 computers because of Vista. And while Vista has come a long ways, it's still bloated,less efficient and will run your applications slower with your same hardware. I would recommend staying with XP. Most are skipping Vista and waiting for windows 7
I hope that helps you.