If you want to do things manually, here is a decent resource Here

or Here is another resource with most of the various antispam /content filters for Exchange 5.5 and 2000.

**We've used Scanmail, easy rules based spam filtering and/or add your blackholes**


but most importantly, make sure your service packs are up to date and obvious exploits are closed off, last thing you want it to become a SMTP relay for the spammers. Using your own rules set for spam and content, though is usually best