Hi solodocmom,
The AC sales department is correct that it is unnecessary, but I bet they have a server. But, it is true that P2P is fine. If you look at some of the past threads on here (and there are many), you will see many differing points of view. All you will need to run AC at the minimum is a good machine that can share the database to all the other computers. That is easy enough. You can always go to a server/client domain setup later.
I, personally, prefer using a client/server, but this is for many reasons, not the least of which is it is much more robust for EVERYTHING on your network. I think too many times on here, the conversation revolves around Amazing Charts and Servers and not your practice management, scheduling, AC and other programs that require speed and redundancy.
But, to answer your question rather simply, if you go with P2P, you should use at least 2GB of RAM on the computer with AC, if not more...some motherboards are limited. It also depends on your OS, WIN7 will require more RAM than XP Pro. Like RAM hard drive space is extremely cheap. So, while 80GBs would be plenty, I would recommend at least 160GBs or more. Again, the later the OS, the more space it takes, and Microsoft Updates take up space as will your imported items. So, even 160GBs on the server isn't huge. And, just get a decent dual-core or quad-core processor (Intel or AMD -- not Celeron). I generally find the highest speed, then come down a notch or two.
With OS, I would go WIN7 Pro, but others will tell you Home Premium is fine. For XP, please get XP Pro and not Home.
Just a few ideas.
