Hi there,
The first thing that I can suggest you is to check the ACS 5.1 compatibility with your VMware machine, I don't see a VMware workstation in the supported list, at this moment only VMware ESX 3.5 and 4.0 are supported for ACS 5.1:
http://www.cisco.com/en/US/docs/net_mgmt/cisco_secure_access_control_system/5.1/installation/guide/csacs_vmware.html#wp1056218
The ACS 5.3.0.40 is now more compatible with other VMware products, but always ESX:
ESX 3.5, 4.0, 4.1, i4.1, or 5.0 Server
http://www.cisco.com/en/US/partner/docs/net_mgmt/cisco_secure_access_control_system/5.3/installation/guide/csacs_vmware.html#wp1069964
Something else that I advise you to check are the VMware requirements like the hard drive space, the ACS 5.x can only run in two modes Evaluation with 60 GB and full operation with 500 GB.
Rate if it helps!