[CentOS] Yum updates vs current packages

Sorry if the subject is a bit vague. I wasn't sure how to summarize this.

I am building a new server (CentOS4.2) and I am trying to stay with RPM installs as much as possible. The problem is with packages that I would like to keep more up to date than allowed by the repositories. This will be a mailserver doing spam and virus checking. As such, I want SpamAssassin and ClamAV to be as up-to-date as possible. The current rpm for ClamAV is 6 months and 3 releases behind.

What is the best way to keep these packages up to date while avoiding dependency issues in yum?