I used to be a Staples Easy Tech Guy, I can tell you XP is much smaller, and there are those "Ways to maximize XP" books for about $20 that really make the thing fly, especially with 2GB of RAM. If you really want an OS you can shake a stick at, try Linux. It is light as a feather and can really maximize applications, you just have to have a bit of know-how to start. There are no real advantages to Vista unless you are looking for a multimedia PC, which I dont know why anyone would.
XP and Vista operate differently. In my experience (using Vista on 3 different machines - 2 x64 and 1 x86 - since beta right alongside XP and XP64). Vista is much faster in day to day operations. Sure it uses CPU cycles when idle (I'm not using them anyway so why would I care?) and it caches frequently used apps into RAM when they aren't in use so they launch quicker causing more RAM to be in use by the OS, however, it is definately better than XP. The main problem with Vista is that it does not like to be limited on resources. Give it plenty of RAM (2GB minimum) and make sure you have a decent video card and spare hard drive space and it will run forever (each of my XP machines have far more problems than all 3 vista machines combined). The other issue with Vista is that techheads think they are smarter than the developers who wrote the OS, so they go in and turn off all the features that make it better (crippling the OS) and then run benchmarks to prove they are right. Nothing like testing for success to promote self image... Sorry for the somewhat off-topic post on your thread.
I run 4 g ram on vista. Sure if had to do it all over again i would have bought xp pro instead of Vista business OEM. BUT, vista being slow etc is being overcooked. Service pack 1 is in and running on a intel 3.0 intel core2 duo chip overclocked to 3.8 on same voltage, 2 wd 10k raid setup hard drives the speed is just fine thank you.
Relevant non-hilarious video: http://youtube.com/watch?v=lBF10ORzo2M "Vista has turned out to be the most gayest thing in the world" On a more serious note, Vista is a step-backwards from XP Pro SP2. Likely needs two SP's before maturity, similar to XP's early problems.