I tried to install CST Microwave Studio 2006 on Windows Vista platform. Everything went fine but at the last step of installation when it says: STARTING SERVICES, the installation roll backs.
May be you need to check carefully installation instructions. I installed CST 2006 on several computers without an problem and 2008 on two machines. It is not easy installation and you need to be very careful. Also it is helpful to turn off Vista UAC.
I think this version(2006) may not work in Vista.
HFSS 10 also have same problem.
According to my information all latest versions (HFSS 12 & CST 2008) supports Vista.
You may have to check with CST help desk.
Added after 1 minutes:
Also one more thing.
There is one facility in Vista using which you can install older versions of softwares
Check that. That option is I guess in control panel.
Some times you may face this problem as it frequently ask for confirmation if we are going to write in to the system folders like programming files.
I suggest to install in another drive or different folder then you can install in Vista too
This problem will be observed in laptops which comes with pre-installed vista and no another drive except C:\