How much memory do you have now?
I upgraded my daughters machine because it was too slow under Vista and perfomed ok under XP and it is noticeably faster under W7...I was going to upgrade the memory but I didn’t need to.
It also depends on how many features you turn on but the platform is very stable and very nice to use.
Currently 2MB of memory. Although my XP has been relatively stable, it’s not the fastest when I see some Laptops w/Vista and Mac desktops.