10.2.8 is evil
Every so often (rarely), Apple does something so incredibly bone-headed I have to just shake my head. Today is one of those days.
Apple released an update to Mac OS X v10.2.8. The update apparently kills Ethernet networking for some users. I saw this problem manifest itself on Bonnie's Mac.
There are a few ways to recover from this problem. One is to reboot into Mac OS 9 (presuming you still have it installed), download an old Ethernet.kext file from the Internet (once you've discovered what the problem is, how to correct it, and learned where such a file can be found), and install it in place of the updated one.
Another is to find a computer elsewhere in your environment that hasn't been updated, and copy the Ethernet.kext file over to it (by using CD-Rs, for example).
Anyway you slice it, it's a royal pain in the ass, and I'm sure some QA gnome somewhere is going to have his or her ass Steved over this little imbroglio.