To my knowledge, HFSS 13 was never supported on Vista. It was on Windows XP (older than Vista) and Windows7 (newer than Vista), but not actually on Vista.
Whether it actually works on Vista might be a different matter. Very often things that are unsupported do actually work. Often bits of software do not work together, even when they are supposed to. ;-)
In another thread, the guy has indicated that his problem was actually to break HFSS licensing in that Windows 7-64 environment. Hopefully, he will remove that post asap, because illegal software use is not tolerated in this forum.
With all due respect, this is your own personal assumption of what I'm trying to do.
I'm just trying to get my licensed v13 to work on my new laptop (running on windows 7-64 bit), with no helpful materials on Ansys website or any of the technical forums. I even emailed the Ansys sales team, but got no reply yet.
Basically the size of the antenna and the mounting surface determines the workstation specs.
Larger the surface more is time required larger RAM and Graphics required