I have a Windows Vista Home Premium. Before this I've been using XP the whole time.
In my opinion, Vista does have a lot of unwanted stuff. You can get rid of unwanted applications in the Control Panel, but there are things that you just have to deal with: Vista likes to give the screen an "aery" look, which really does make the CPU work harder than necessary. This is why most Vistas need to have a lot of RAM. My Vista laptop has 2 512MB, totalling 1GB, and it works fast enough, so the 1GB that you have should be enough. The difference is that mine has 2, so when some application is taking up the memory off one the other is ready to be used for something entirely different. Parallel processing becomes easier. In your case, since it was originally Windows XP, I'm guessing you only have 1 1GB memory, so that might make your computer slower if you change to Vista. Especially if you like to play games on your computer a lot.
Other than memory and speed, I would say Vista isn't very different from XP. Most of the most useful tools in Vista are the same as XP, so there's nothing surprising and amazing about that. Sometimes I come across softwares that don't support Vista, which is annoying, but I guess that would change as more people start using Vista.
Well, good luck making your choice, but here's my opinion: if you have an XP, and have no problems, keep using it. Vista is not amazing enough to deserve a risk of making your computer slower.