I was actually curious about this myself, because I am thinking of upgrading to a 64 bit processor and OS. If I understand you correctly you want to know if you can run PS in 64bit WinXP or on a 64 bit distro of Linux.
I still wonder if you can't download the source code, the art, and the engine and compile it yourself, but that does seem like a bit of work. I am fairly computer savvy myself and I still have never been able to download the entire source code from sourceforge.
Best of luck and I will keep an eye out for responses.