XDM and Variable X Server Configurations?

[John Stevens <jstevens@c549076-a.ftclns1.co.home.com>]

Greetings,

I have Debian 2.2 installed, running XFree 3.3.6.  The video card
is a Voodoo3 3000.  I have the neccessary setup to do accelerated
3D on this card all figured out, except for one minor, irritating
little point:

I normally run true color, 1280x1024 mode.

To be able to use the accelerated 3D, I have to logon as root,
modify my xdm/Xservers file to set the -bpp 16 parameter, ctrl+alt+del
on the xdm screen to restart, logon, then ctrl+alt+Numeric+ to get to
a 640x480 resolution to be able to use the acceleration.

My question: is there any way to set up xdm so that it gives me a
menu that allows me to choose different X server configurations?

Or is all this manual mucking around the only real way?  I cannot
afford to run two X servers at the same time (insufficient memory),
so if there is any other way, thanks in advance for the suggestions.

John S.