It actually never gets to a screen of any sort so it's quite early in the piece. It must be during a BITE check of the vGA card (because that's normally the first text info to appear on screen). Instead of continuing its hardware head-count it just dies on the spot. So my theory is that instead of finding the card it's finding some sort of conflict between the VGA card and the parallel port (but strangely enough it affects both an AGP Riva TNT7700 and a PCI Matrox Millenium 11 VGA card). You hear a click in the monitors as the green light gives way to the orange status light - and the boot cycle stops, leaving you with the PS fan whirr only.
Once you remove the Zip-Drive's data-cable it is OK. The zip-drive did work in this machine, on this motherboard (and works well on other machines as well (but we don't have any other win 98 machines to try it on.
I've used the unified Omegaware software (drivers included). Version 31 and earlier v28.... Both give the same symptoms.
It's annoying because the case has no room for an internal zip drive.