Hi Roberto,
Not really an answer to your problem, but why not stick to the 32bit release then? According to the guys who really know their stuff, there is no real benefit, performance wise, to run 64bit.
Speaking for myself: I have 2 AMD 64bit MD's, but both of them are installed as i386 MDs, and they work mighty fine, alpha blended and all!
Greetz,
Reint.