PKA and Bill
All of the above are good advice.
I have 2 offices, one is on a server and one is not. I am frugal as well.
I have computers as slow as a 40 Mhz pentium 2 (mainly for faxes and old vaccine program, but it does run AC well) to Server with a Dual core and 2 Gigs Memory and 500 G hard drives (never got around to upgrading it, works well). Currently my P2P system is running on a XP system with dual core.
I had been building computers but recently have found a number of cheep (<$100)2.4-2.6 p4 machines, and have been upgrading them recently. Impressive increases in speed because of gigabit wiring, not necessarily from the computers themselves.
The bottom line is for a cheapskate (I am quite frugal) a fairly minimal system will work reasonably well. For more money, it will backup easier, run somewhat faster and interact in a more consistant manner that probably takes less tweaking.
Hiring an IT person would be a good thing if you do not have the knowledge or inclination. Mostly a 1 time thing for setup, although there is ongoing maintainence. They will guide you as to both hardware and OS's. While I never used one, I had friends who I consulted and read a lot, along with what I already knew. Without help I would have been stuck many times.
Server is probably better, but dedicated regular computer will work well. You need to decide both how much you will spend in the short run, and how much you will spend in upkeep over time. You need to have backup backup backup.
