Using the Program "Everest" I get this information
CPU name Intel (R) core(TM) 2 Duo CPU 4600 @2.4GHz

Instruction set
64bit x86 extention (AMD 64, EM64T)

Motherboard Dell Optiplex 320

Front side Bus Properties

Bus type-Intel GTL+

Bus width 64-bit

So can I install Windows 7 Ultimate 64 bit?

Thanks