What you'll need
To install the tools at all, you'll need a computer that can run Matlab. For analysis, the code should work on any platform.
If you want to run visual stimuli, you'll need a computer that runs the Psychophysics Toolbox. If you care about high temporal fidelity, you'll also need a good cathode ray tube (CRT) monitor like a Sony GDM-520 (discontinued; Ebay is the best bet).
If you want to communicate remotely with a computer (such as communicating between a stimulus computer and an analysis computer), then the 2 computers will need to have access to the same drive. The easiest way to do this is to mount the same shared drive on the 2 computers; this drive can be physically located on a server to which both computers can gain access, or it can be on the analysis computer itself. The software program DAVE allows OS 9 computers to mount shared drives on Windows XP machines when the XP Firewall is turned off (not sure how DAVE does with Vista or Windows 7 servers). (Note: there is a system for communicating with sockets that should be relatively operating system; it runs on Mac OS9, Mac OSX, and should run just fine on any unix and on PCs. However, in testing with a Mac OS 9 stim computer and a Mac OS X analysis computer, I have found that sockets are not nearly as reliable as file systems for really long-term communication, and I don't recommend using them. It's possible that the library could be made more reliable with more effort.)