Forced an install of the latest Intel graphics chipset drivers (Ver:14.32.4.4926, 2008, for XPPro 32), regardless of its complaints that it had some sort of custom driver build. With the latest drivers and after a restart, the WED Level Editor seems to be running fine now. Haven't yet found anything broken as a result of the driver upgrade, so things are looking good.

If it is of any significance to anyone else with a similar issue, I also disabled all display adaptors except the one in use.