About the GPU driver Vista was installing, I realised it was an older version of a SiS driver. I tried again with the more recent one, 2.93, but this time installing directly from the device manager, and I now was able to get past the 1024x768 resolution when selecting higher resolution ones (it would just stay at 1024x768, so if I selected a higher one I would had to go to the monitor edges with the mouse to see the rest of the desktop, and that's why I assumed my VGA BIOS couldn't render higher resolutions).
I also modified the 2.93 driver to include more resolutions: 1280x720, 1280x800, 1360x768, 1400x1050 and 1600x900.http://www23.zippyshare.com/v/56437157/file.html
(install the driver throught device manager, ignore the invalid certificate error warning)
I tested it on Vista and Windows 7, both x86. Unfortunately, I have no idea how to enable the 1366x768 resolution.