I keep hearing that Win7 and (less surprisingly Win 7 64) are "incompatible" with certain models of computer and it isn't entirely true.
What may be true is that drivers for certain motherboards or components (perhaps as basic as hard disk controllers) are not included in Win 7. If Win7 doesn't pause during install to allow those drivers to be added manually (though who would have them handy except RAID or SCSI users I don't know) that will cause a problem.
Some component manufacturers and chipset makers have failed to provide drivers for Windows 7 for certain of their products, particularly the older ones.
This tends to support the theory (and the inflated price of a copy of Windows retailed separately) that it is better not to upgrade Windows on older equipment but instead to wait until you get it included in the price of a new machine which has been tested with it.
I can understand you fleeing Vista but, having tried Win7, I don't think it's worth the effort of learning new ways to do the same old things that XP already does, let alone faffing about with drivers for components that previously worked okay. As for going to 64 bit, I think that's just asking for trouble.
The time to switch to Win7 is when components you want to use don't have drivers for XP -- which will be some way off, hopefully.