Sorta OT Mac G4 TCP question

Have a G4 400 running OS9.2.2, 1G ram, used as an 'appliance' computer in my studio. As a result of a bizarre problem in getting a new software package to authorize (so far the company can't figure out why it's broke - !) I need to hook the Mac up to the Rest Of The World and download a bunch of patches and crap. To date, I have never used this computer on-line - so I drug Cat5 cable in from the switch, hooked it up, and Voila! 'That Which Communicates' is also completely hosed. I get "Internal error #300" and "Mac OS error -23" pointing to a funkyness on the part of the TCP/IP stack / driver / panel / thingy, as far as I can see from looking up endless pages of error codes. And I've made all the settings recommended... also, the cable is known good and works perfectly when drug back into the office and hooked up to this laptop upon which I type. I've spent the better part of three hours turkey-ing about with this - and I have *way* too much invested in it to just heave it into the desert like I want to - so I thought to bend the List Protocols a bit and see if anyone has one of those "Oh, yeah, here's what ya do..." type responses. More info will be cheerfully supplied, I don't know what elese to add. Cheers John