There's a new cat in the forest when it comes to keeping your /usr/ports tree updated - portsnap. It does it a little better than trust old cvsup.
Good discussion about it here on the PC-BSD forums:
portsnap instead of cvsupA short discussion about portsnap and why it is better than cvsup:
FreeBSD PortsnapAnd, of course, the FreeBSD.org doc page about it:
Using Portsnap

Is portsnap available to versions prior to 6? I'm using 5.4 myself at the moment with no real inclination to upgrade.
I think you can just install the one found in the /usr/ports/systutils . It comes pre-installed in 6.0, but for earlier systems, you should be able to use the port.