BeOS does not yet support dual video cards. If you do have two video cards installed for the sake of Win98, and BeOS always boots to the secondary (el cheapo) card, simply delete (or move to a backup folder) the secondary video driver file from /boot/beos/system/add-ons/kernel/drivers /bin.
I had this problem when my old Matrox Millenium. BeOS was loading its driver before the driver for my shiny, new Voodoo3. Canning the Matrox driver caused BeOS to recognize the Voodoo3 instead. Sure beats pulling the card between boots…