XFree86 Config failure on laptop with external monitor
 

I have a toshiba portege 7020CT with FreeBSD 5 recently installed (dual boot with windows NT4). The laptop screen is broken so I have it hooked up to external monitor, keyboard, and mouse. I have so far been unable to get XFree86 to configure correctly. I did not configure it while I was installing the OS since I was concerned I might have issues with it, so I have been configuring it by running the various xfree86 config utilities on the machine. The model and make of the video card (neomagic) is correctly detected, and both keyboard and mouse are detected correctly - yet each time I try to configure the monitor, either by editing xFree86Config or by using the graphical configure utility, I get a message that the configuration failed.
Any ideas what might be going wrong? My completely uninformed guess is that maybe XFree86 can't autoconfigure the external monitor and is trying to configure based on the specs of the (broken) laptop screen? If that's the case, is there a way to force it to configure the external monitor? That may even be a kernel configuration issue?
Any help would be appreciated.
Thanks,
Philip