Bingo!
The yum update took care of it.
Oddly enough, until I started my new job 2 months ago I'd always been in the habit of running 'yum -y update' first thing after installing Fedora or CentOS. But the product software we develop does not like that very much so I got out of the habit very quickly after blowing up a machine by doing that :-/ Fortunately it was not a production box.
But I do recall actually that I'd done it on my desktop at one point shortly after starting.
Thanks all!
I'm going to probably re-install my own Vista box here at home with Centos 5.3 64 bit, so I'll try the other method on it. Um, maybe something for a whole new thread, but does CentOS support eSATA? My desktop at home here has a port for it, and the USB drive in question does eSATA as well. Makes it SOOOO much faster when connected to my box!