I recently upgraded to Win7 Pro (64 bit); I still use Combustion. Combustion works OK under this setup; of course it’s still a 32 bit app, so you don’t get to use any more memory than before. But: there is a 64-bit Kona(Xena) driver, so the framebuffer works. The main bug I’ve noticed is that Combustion does not remember UNC paths in the browser. It is OK to use them in comps and net-rendering, you just have to re-navigate when importing new footage. Or, you could just use mapped drive letters. This may be due to my network being without DHCP (I use a small workgroup). Sapphire plugins work, and I have not noticed any more crashes under Win7-64 than XP-32.
-Jeff