RE: What will give me higher quality audio 64bit or 32bit
No audible difference between 32- and 64-bit OS. SONAR computes at 64-bit regardless, and files are saved as 32-bit floats. So for audio quality, it really makes no difference.
The reason people go with Vista 64 is to be able to use RAM beyond 4GB, helpful if you use a lot of samplers. Many vendors still do not have 64-bit drivers, though, so if you don't need the extended memory addressing you may avoid problems going with 32-bit XP.
There may be a subtle improvement at 96KHz versus 44.1KHz, but if you have a good interface it's probably not worth the overhead.
All in all, I'd stick with 32-bit XP and record at 44.1KHz, as least for now.
All else is in doubt, so this is the truth I cling to. My Stuff