Server Suggestion

We're going to be setting up a freeRADIUS server to service around 400 simultaneous connections. (500 AP's, 4000 users, about 400 online at once) Accounting info would be on another different server.(Not part of FreeRADIUS) What's a good server for this? What's more important? Memory or CPU? I was thinking a dell poweredge 750, 2.8Ghz, 1Gig of RAM, 73G drive. Thoughts?