Um Kiwi...if you have Xeon 5130s in your machine...they're 64-bit processors...they'd run x64 Windows 7 just fine.
http://ark.intel.com/Product.aspx?id=27216
You were probably getting x86 in the runtime because your current environment was x86, not x86-64 (or x64 for short).
For the record though, PAE would enable all four GB of RAM, but at a significant speed reduction...you're better off torrenting a 64-bit copy of Windows 7 Ultimate and then using your valid license to install it (yes, I know torrenting is generally frowned upon here, but there's nothing illegal about this so long as the license is valid). For the record, Windows licenses can be used for either 32 or 64 bit software interchangeably.