I was a beta tester for XP before it came to market, from beta 1 onwards. I can tell you, I did not enjoy it. I was using windows 2000 alongside it, and during the first beta, I would be relieved if I could go back to it. I had non-working drivers, or partially working drivers (the USB DSL modem was a partially working one...imagine how much fun that was) I had some filesystem problems under the beta, which meant that anything downloaded under the beta was simply corrupted under any other filesystem....and I can go on and on....
As for you needing a new system.... To be honest, I have not noticed that much of a difference between 32 and 64 bit.... Though I have really noticed the difference between my old athlon x2 3800+ and this set up. I'm guessing you will notice the difference too, especially if you decide to go for a quadcore. If I were you though....I'd hang on for 2 or three more months...just till the core i7 is there. Not that you need to get that immediately, but its release will mean cheaper older chips...and AMD will still want to be able to compete.....