My quadcore desktop can run Win 7 easy enough according to the test. I had to make some effort finding a XP-licence when I had my system build; Vista was all that was available. Luckely the store had OEM license left, and they gave me the full XP-disk I have my DAW running on my desktop and I use some hardware for which the software support ran out with Vista (no Vista-drivers available).
I'm intending to stick with XP for my DAW for as long as I can. When my desktop (or my wife's desktop, whichever comes first) should need replacement, I seriously am considering buying a Mac.
***runs into garden to add fertilizer to the moneytree***