The server itself is a P4 2.8 Ghz, 512 MB DDR266, and a 7200 RPM hard drive. As mentioned previously, we run Windows Server 2003 because the Steam HLDS for Linux eats CPU cycles for breakfast. If you DO want to run Linux, you could find some help with configurations in the Server Discussion section of the official NS forums.
You will want to set a maxrate, as after a certain point you're just wasting bandwidth...you'd have to get a post from LB himself on that one however, as I'm more of a webserver guy than an expert on HLDS.