As Jimmy said, a P3-500 should be fine. However, there are certain things that take a lot of processing power no matter what OS you're running. Amongst these things are encryption and audio/video encoding and decoding. Well, maybe I should say that they'll take about the same CPU power regardless of OS. My point is that if you're just running some web servers or file servers you'll be fine. However, if you start encoding mp3s, running an IPSec endpoint, and playing videos with CPU-intensive codecs, then you might run into problems.