*** DISCLAIMER: I am not a Millisecond Software representative, so this is not to be taken as an official statement. ***
(1) Generally, installing and running Inquisit in a virtual machine seems to be an unsupported usage scenario. The FAQ on millisecond.com (http://www.millisecond.com/support/faq.aspx#mac) states:
Does Inquisit run on the Mac?
It might work on a Mac running a Windows emulator such as Virtual PC. However, we do not support or test Inquisit on the Mac.
(2) It's been indicated in the past that there will eventually be a native Mac version of Inquisit. As far as I know, no specific details or dates have been announced yet.
Being a rather tech savvy guy, here's my personal take on the matter. It all depends on what exactly you mean by 'running Inquisit':
(3) Can you install the software in a virtual machine and use it to develop experiments that can be run on other PCs? -- Most probably yes. Although you might not be able to properly test these experiments / audit timing when using a virtual machine (read on for an explanation).
(4) Can you install the software in a virtual machine and use it to collect data from subjects? -- Most probably no. Let me try to clarify. Your scripts might actually run in a virtual machine, in a sense that whatever you have entered will be displayed on the screen, input will be accepted and recorded, etc. But here's the thing: If any aspect of your research involves some sort of critical timing -- i.e. if you need to care about exactly *when* a stimulus is presented and precisely how long it takes a subject to respond to that stimulus (i.e. if you want to analyse millisecond response latencies) -- I'd strongly discourage running in a virtual machine. Applications like Inquisit achieve their precision by accessing the computer's hardware *as directly as possible*, and -- simply put -- that's obviously not feasible when running in a virtual machine (where the 'hardware' is really emulated by additional layers of software). If, on the other hand, you're not interested in response latencies and timing precision at all (e.g. if you just want to set up a simple survey or the like), you might be fine. But then what's the point in using Inquisit, anyway?
(5) There's an alternative if you have one of the newer Macs sporting Intel processors. These are able to install and run Windows *natively* (i.e. on their real, physical hardware without any virtualization) via BootCamp. In this scenario your Mac is essentially identical to any other PC running Windows. With a setup like this, you should be able to both write and run scripts to collect meaningful reaction time data with Inquisit. I also feel that this actually should be a supported scenario, although I can't vouch for that.
Hope this helps,