What is the proper way to invoke GDM at start-up

Hello, everyone,

I installed Gnome and Gdm from snapshot packages (as of April 24).
IBM ThinkPad A30p, OS snapshot April 20.
Everything's OK, but I'm having issues auto-starting Gdm.
If I put /usr/local/bin/gdm into /etc/rc.local, it starts, but
ignores the keyboard to the point that I can't even do ctrl-alt-fn.
Mouse works, so if I, say, select xdmcp chooser, then cancel
(i.e. restart the gdm), keyboard now works fine.
After a healthy dose of googling and man pages, it looks like
the problem is in tty allocation. At least on linux gdm can
take an additional argument like vt7 to grab tty7.
if I put gdm into /etc/ttys, it works (keyboard is OK), even
if slow on start, but complains along the lines "server failed to restart"
to the logs on logout/session end.

Could somebody please enlighten me on what is the proper way of
starting the gdm automatically on OpenBSD? And why xdm works fine from /etc/rc
and gdm doesn't?

Thanks.
--
 nickf3