What Operating system are you running?
Sounds checky, but if you are running WM2003SE you can use SE_VGA. It works great, but you have to do a soft reset eberytime you want to switch back and forth between modes.
Here's the link
http://www.pdagold.com/software/detail.asp?s=496
or just google SE_VGA and there are a number of sites that should help you out. SEarch among the boards here and you will find a really good guide.
Here is it-I'll be nice-
http://www.aximsite.com/boards/showthread.php?t=98163
Good luck.