Getting RedHat updates

[m.roth2006 at rcn.com]

Ok, first time I've tried to get an update from Redhat in a couple of years, and the first time from work. The site's changed, so I can't find the download the way I used to. Now, I'm behind a proxy and a serious firewall (or, more likely, several layers of them, *sigh*).

So: I tried 
up2date -d mysql-4.1.20-2.RHEL4.1.i386.rpm

and it couldn't find it. So, what did I do wrong? I want the one security fix, and *I* want to install it, so I can back it out if it breaks something the developers need.... The man page isn't clear enough to answer this (for example, what the hell is a "channel"?)

     mark