64 bit OS support on Dell Optiplex 745

Hi all,

I'm having an issue with a Dell Optiplex 745 (desktop). The CPU installed is the Intel Pentium D 800MHz 3.4GHz. In the BIOS it states it is 64 bit technology, however I do not see the option under performance to enable VT. I've tried upgrading the BIOS to the latest version (2.6.3) but alas to no avail. Has anyone come across this issue before?

According to the tech specs this processor is definitely enabled for VT and is confirmed in the BIOS also but I cannot install any 64 bit OS onto it due to not being able to enable VT.

Please help??