Ok llamas, here is the authoritative answer. Authoritative because I've done it. 🙂
A P200 w/ 80 ram would be a fine dedicated Q3 server. RAM does matter, but the OS you are running also matters. I'd say that on average, you're going to need about 20 more MB of RAM in an OS with a GUI (i.e. windows) than you would if you ran the Q3 server on a console based OS (linux / freebsd).
Last year, while pimpin' the dorm connection, I had a Q3 dedicated dm17 only server using a heavily modified pak file (5 mb total from 400+ mb) running on a FreeBSD box with a Winchip 200 and 24 ram (yes you read that right). The max clients was set to 8, and it would NEVER lag due to a lack of hardware even with 8 clients playing. (Now Berkeley's connection on the other hand would have issues.) I needed to use the same computer with 48 ram to handle the same number of clients when the server was run in NT4. Also, be sure that the network card you use is PCI as they have much lower CPU usage than ISA's.
Now the other nice thing about having your Q3 server run in a console based OS is that you can just telnet / ssh to it and enter commands, settings, etc. as if you were directly in front of it. If the server was far away, this could be a real time saver.
Good luck with the project. I'd say that you could do 12 clients on 1 map, max.
~bex0rs