So I've tried installing both the OES Client for Windows 4.91 SP4 (~35MB
download) and the smaller (~21MB) Novell Client for Windows 4.91 SP4,
but in both cases, the Initial Novell Login window does not appear when
RDP'ing to a workstation.

I use RDP to build workstation images, as I keep the thing setup in the
server room, which isn't a fun place to hang out w/o some additional
clothing, so RDP'ing to it from the comfort of my office is much
better. On SP3, when I RDP'ed in, I'd get the login dialog, just as if
I was at the console. Nn SP4, it just auto-logins straight to Windows,
bypassing Novell completely.

Is there an option I've missed someplace that didn't get carried over
in the SP3 -> SP4 Upgrade? Maybe a GINA agent for RDP isn't configured