Here is a good article on understanding some of the things that vista is going to impose on you!
I would like to also mention that windoes Vista at bootup will use 700-750meg of memory. Currently an xp machine uses around 200-300, and a gig or 2 of swap file on your hard drive. To run vista you will need 2 gig minimum of memory. Most machines these days have 1-2 gig.
A good read. Be warned it will make upset. Due to vista's strictness with hardware, your PC hardware costs will increase and have more tecnical difficulties!
http://www.geekzone.co.nz/juha/1908