after searching through the whole forum and having a go myself,
finally gave up and concede to the fact that onboard video JUST can't do 800X480
finally resorted to using a PCI video card, which, is HARD to come by. PCI express may be, PCI is hard to find (just like usb gameport. "Game port? who uses game port nowadays)
i was lucky to have a PCI extension board lying around. but you first have to change the heatsink on the board to something shorter.
the card i managed to find is Inno3d's MX440 based. the driver allows you to define custom output resolution.
now in the process of installing. will post when i manage to get it to work