PIII vs PIII XEON?

I need to spec a server to act as an SMS 2.0 Site Server plus SQL Server 7.0

The server is for a relatively small firm (200 users), and cost/performance need to be considered.

Ideally I’d like to spec a server with dual PIII XEON’s @ 700Mhz, but I may have to settle for dual PIII’s @ 866Mhz.

I’m uncertain as to the benefit of the XEON processors. Could anyone offer any advice?

Thanks.