There was a software and hardware solution called Siamese that would do about what you ask. IIRC there was a version 2 that did NOT use a PCI card - I don't know how that version worked.
I believe Siamese was limited to Windows 98 on the pc, but I could be wrong (It's been a long time)
This setup appears on ebay every now and then, but sure isn't what you would call a hot item.
