wftomlin, welcome to the Seven Forums.
There is nothing you can do in Windows (or Linux for that matter) to get around what you are trying to do, it is entirely a hardware/bios issue. Not sure what is in the paper manual but the PDF version from here, ASUSTeK Computer Inc. - Motherboards- ASUS P5G41T-M
has enough to go on for the most part. The problem is that in a lot of cases the onboard video gets disabled when a video card is detected, and usually not much that can be done about it. In the case of your motherboard it may be possible if you go into the bios to the Chipset section and set the "Initiate Graphic Adapter" to [PEG/IGD],
No promises but that should allow for the onboard video to be used at the same time as the video card.
P.S. Does your GT 200 not have a HDMI port as well? If it does and you only have one monitor connected to the card, you can use it instead of trying to get the one for the onboard video to work.