You can use IgnoreEDID in order to make it get 1600x1200.
HOWEVER - The 6106 and 6111 drievrs are broken on many Toshiba laptops, including the Satellite Pro 6100. I have the same laptop. You can either use older drivers, and ignore EDIDs, use 1400x1050, or set a modeline for 1588x1200.
See this thread for more information: http://www.nvnews.net/vbulletin/showthread.php?t=32997