I am running g4.5 on windows 7 64bit. It does work. As far as all the people who are trying to steer you away from 64bit, I will just throw in my .02. I've been running Windows 7 64bit for a while now, and have yet to run into a compatibility issue with any software that I've installed. The only 64bit compatibility issues that I have ever run into was way back with xp 64bit when it was first new, and then a few in the beginning with vista. That was probably because (as ShaneLittle mentioned) it was not really a standard. To say that it's still not a standard is just not true. 64bit has been around for 3 generations of windows operating systems, and pretty much every other operating system out there has a 64bit version. Personally I don't worry about it anymore. If I'm using 4GB of ram or more in my pc, I'll use a 64bit operating system (there are more advantages than ram support, but ram is the obvious advantage), if I'm just throwing together a little file server or something, I'll just use a 32bit operating system.