The specification on the Intel website suggests that your CPU doesn't support hardware virtualization (look for the 'Virtualization Technology (VT-x)' setting):
http://ark.intel.com/products/36547/intel-core2-quad-processor-q8200-4m-cache-2_33-ghz-1333-mhz-fsb
Hardware virtualization is a requirement for 64-bit guests in VirtualBox, and there is no workaround.