Well if you can wait a few months I think that would be the most optimal option. If memory serves, I believe the time frame for the newly revised B3 chips is around May sometime. But to be honest I don't know how that information will hold; AMD seems to be putting out nothing but bad news about delays on their CPU front nowadays
Although recent rumors suggest their 45nm parts will come out in 3rd Quarter of this year, so around July-September. However I'm taking these rumors with a grain of a salt, but only time will tell.
Certain softwares are affected with 64-bit. I honestly can't tell you which ones, you'd have to do some searching to see which have drivers and are compatible. But I'd suspec that if it is old software, it probably wouldn't run.
As for games, there have been issues with some games in 64 bit. And I'd venture to say the older the game the more problems there would be, but I don't know. I do know however that older games don't even run under Vista period. For instance I cannot get HoMMIII to run on this laptop, which has Vista.