VISTA -Video troubleshoothing

I have a Dell Optiplez GX745
Intel Core 2CPU 6300 @1.86GHz
2GB RAM
32-bit Winsows Vista

I am not allow to run a third display on my system. I have a Ati Radeon 9250 and a 256mb ati radeon x1300 pro. I can use one or the other, but i can’t use both. I try splitting cables and that works for two monitors but not for the third. The Device manager shows the card as disable. Any ideas will be greatly apreciated.