Doug,
The primary, and for me, deciding, advantage of 64 bit is the maximum amount of RAM you can use. For all Windows 7 products,the Max usable RAM is somewhat less than 4GB. For 64 bit Windows it is 16 GB for Home Premium and 192 GB for Professional and higher. There are technical ways around this, but it's not simple. See:
http://msdn.microsoft.com/en-us/library/windows/desktop/aa366778(v=vs.85).aspx