Applying Apple's patches was a little more involved - my first approach was to download them on a Mac, create an ISO image (Apple's tools can do this:
hdiutil makehybrid -iso -o OS42patches.iso OS4patches
rather nicely) then put the ISO in the virtual CD-ROM drive. While the tarballs unpacked correctly, the package they contained was corrupt. So I downloaded the patch (OS42MachUserPatch4 being the latest one, containing the SVGA driver and the y2k fixes) to a Solaris box, then used FTP to get it over to the OS4.2 PC (now that we've got network). This was more successful, and the patch could be installed.
So, now we're fully patched, pull out the "Default VGA" driver and put in the VBE (VESA local bus) one, using Configure.app. Let's choose a low resolution for the first boot, just in case; reading Apple's notes, we should be able to check which modes are available and change at boot time anyway. So I've gone for 640x480x8 (i.e. 256 colours) for the first boot... and it hangs here.
This is actually after I typed "VBE Check"=Yes at the boot prompt, and it didn't show a list of modes...so something's not quite right with the VESA driver. I'll leave it overnight in case it decides suddenly to boot, but I think that reverting to Default VGA is, for the moment, the order of the day.
Edit 2006-04-10 17:36 GMT - some history revision, correcting a spelling mistake and therefore pretending I've never heard of visual basic for apps :-)