This thread is from last week, similar questions:
http://www.cgarchitect.com/vb/16067-athlon-mobile-64-x2-vs-64-fx.html
In the end I bought an off-the-shelf Toshiba so I wouldn't be waiting 3 weeks to get the thing. I had to drive to a CompUSA and wait 1/2 hour while they swapped in the new RAM chips to get 2GB. About $3000 with the RAM.
However, the Intel duocore chips are 32 bit I think. But not many of my day-to-day apps are 64bit, so it's working very well.
The only issue I have is that since this thing is a consumer machine, it has lots of crap on it I really don't want, like 'AOL tryout' and it will take some time to get rid of all that.