Nowadays, if you want to be able to run 64 bits guests in the hypervisors or hosted vmware products, there are some hardware requirements you must satisfy.
First the CPU must be Intel EM64T and VT capable or AMD64 (revision D or later). At the end of this post there are useful links about what processors support this virtualization technologies.
If the CPU is Intel VT capable then it must be enabled on BIOS. To be really sure is better power off and power on the system after changes are configured like this vmware doc recommends (checking it carefully is highly recommended): http://communities.vmware.com/docs/DOC-8978
Useful information about Intel and AMD virtualization features and CPU features finders: