You can't upgrade via Express Upgrade, it is for new systems purchased on or after October 24th.
You have to buy a full or upgrade version when Vista is released on January 2007 (if it doesn't get delayed).
Having an ATI card has nothing to do with the display identifier. I have an X1400 currently and can see identifier LPL0000 just fine.
Go to Device Manager > Monitors > Plug and Play Monitor > Properties > Details, in there...