Not sure about 3.0, but I know 4.0 works. I've been using 4.0 on a couple x64 machines and it works just fine.
Do you need 3.0 for any particular reason? Or do you just prefer it to 4.0?
Actually, I'll try to see if I can install it on an x64. I don't have an x64 machine setup right now. I had one yesterday and then I switched over to Win 7 build 7260 x86. So it'll be a little bit (hour or so?). Maybe someone else could give it a shot?