We use Exchange 2000 on our back-end server which is a Compaq DL380 w/4gb memory. Currently we use McAfee's Groupshield on this unit.
I'm not sure on an external call from Ex 2000. What was your experience with spam before and after implementation of SA?
You might want to look at http://www.christopherlewis.com/ExchangeSpamAssassin.htm for some information about implementing it with Exchange.
Bret