To very crudely elaborate on what GM correctly said about programs, you're not going to find sharing hard drives is going to create a "master computer" or two interchangeable master computers.
Using programs remotely depends on how much interaction the program needs with you and the computer you're working on. If it's just a case of it taking the information from you, such as a file you want the program to process automatically (such as dragging and dropping onto an executable - on the program's home computer - that performs a simple, preset function) and then you fetch the results, it can be do-able. But, though some programs can take remote input, most, I would definitely think most games, are set up to read the input from the keyboard, mouse, joystick, whatever, on the computer they're running on, not the remote computer. The more a program has to interact with either the hardware or the file system on the remote computer, the less chance it's going to be able to work remotely. Mostly, it's problematical and you shouldn't get your hopes up. The vast majority of home network use is file sharing, not file processing.
You would need to setup one computer as a remote terminal and the other as a server. Although, you might be able to do that both ways, maybe with different interchangeable accounts. But one would have to clearly be the master and one the slave for each individual transaction. There's probably software to do that or Windows settings, but home users don't usually do it. If you're going to set it up as a permanent situation with one always server and one remote that would be easiest. Basically, someone may be able to suggest an easy solution, but it sounds like you're going to a lot of trouble. I would just copy all compatible standalone programs from one to the other and copy all installers that were cross compatible and just accept that it might not be worth the work to setup complete program sharing. If it would even be possible.
Especially since the main difficulty you face is the significantly higher security restrictions in Vista, not all of which can be easily turned off. In fact, it might be easier to do it with XP and Windows 7, which suggests how much of a problem Vista compatiblitly can be. Just file sharing is a lot more likely than jumping through all the hopes of (theoretical) program sharing.
