Skullz,
Welcome to AC and thanks for your post. Adam gave good advice, although I will challenge him why get Vista, if you aren't going to use all those cool effects like Aero. Hell, you may as well go back to using the boring XP.

Unless, of course, Microsoft sent like ten to you, but you know they won't do that.
I think his question is the following. If your "base computer" (Server) has 2 GB of RAM and good hardware, etc. that meets the minimum requirements of running AC, can you get away with less processing speed on the clients? Is that correct?
Before, I answer, I must agree with Adam, that your answer is a little vague and also your answer will always be a little like a seesaw. Imagine that the faster your server is (goes up) the less powerful your client may need to be (goes down). It's always good to make your server your best and most powerful computer. However, unlike the thin clinets of the past, you aren't running the applications on the server. You are still running AC on your workstations. Therefore, the faster your clients (workstations), the better your performance with AC will be. If you only have 256MB or 512MB of RAM on your clients and you have AC open and you pop open Word and two Internet Explorers, your performance will go down. You also need processor speed to make your calculations on your computer. As you know, the three most important things on a computer are the processor, the hard drives and the RAM. The latter two are so cheap, you may as well go with the theory, "the bigger, the better." If you can get 2GB as Adam suggested on each, get 2GBs. If you can get 3GB get three. Just remember how you configure the RAM is important so you have to look at your system board's manual or ask someone before just filling three DIMMs (slots) out of four. And, also remember that 4GB = 3.2GB if running 32 bit OS which you are. So, 3GB is optimal if your system board takes it. It is always a little more difficult to increase your processor speed as you don't just add them and going to better processors sometimes means getting a new motherboard (system board).
Remeber with AC, all of the data is transferred back and forth. Your server will send and receive from the database, but that's it. Most of the work is done on your client.