When investigating this for our organization I wrote a report that showed me all my Computer Model Numbers.  Then I referenced the support sites for each of our hardware vendors.  As I so dissapointingly found even though a computer's hardware can handle a 64bit OS doesn't mean that the manufacturer is providing 64bit drivers for the OS you're looking to install. 

That said, my guess is that if you're thinking of doing 64bit Windows 7 going forward that you're probably pretty good to go with anything purchased in the past couple of years.  Still it'd be a good idea to double check with your hardware manufacturers to see what they'll offer you in the way of drivers, no matter what your plans.

From my understanding most, if not all Core 2 duos are 64bit CPUs. According to Wikipedia the Core 2 line is the 64-bit consumer line CPUs. The wikipedia article had a link to http://ark.intel.com/ which has a list of all of their CPUs models. I only checked about 6 or 7 of the Core 2 desktop models and every single one of them were listed as having a 64-bit instruction set. It might also be possible to pull the CPU model number and do a case statement in your SQL that lists 64bit CPUs only, though I am pretty sure doing that is not practical. I agree with MBHarmon though, most CPUs that have been manufactured by Intel use a 64-bit instruction set so it might be safe to just trust that the report is showing 64-bit CPUs. 

~Sean

 Thanks for the thoughts guys.  We need a ballpark guess only, so i may do something quick and dirty just looking at the cores/processors per machine.

 Jim,

I believe that is the issue!  i will be testing this tomorrow.