I’m currently running an Intel Core Duo that is about a year old and it simply isn’t x64 capable. This is in response to the poster who “wished Microsoft had only released an x64 version of Vista”. They would have left a lot of us out in the cold.
With that said, you can see why many hardware manufacturers haven’t been too quick to come on board. x64 Win XP has only been used by a select few to date because you would have had to buy fairly high end processors to even run it. Only now are mass consumers finally being offered processors that can support the x64 OS’s (at least for Intel).