如何在 win xp 啓動雙螢幕顯示設定 ?

You need to download the both the drivers for the onboard chipset and the new pci display card ...
also make sure your BIOS is the latest and support 2 video card ...
then your XP should be able to handle 2 video cards ...
It is not an easy task ... it may need to upgrade BIOS ...
go back to where you buy the new card, and ask for the store people to help
otherwise, don't mess around with this kind of configuration ... quite a tough task
if you are not experienced.