You may not have the 64-bit version of vista which is the driver he linked you to.  You can have a 64-bit processor and still have 32-bit windows. If your display and everythign else is working good right now, you want to make sure you can fix anything if it doesn't work though (installing new drivers and stuff).  So create a system restore point.  I can't tell you how to do this in vista, but if you go to the help section (probably somewhere in your start menu) and search for system restore, it should have step by step instructions.  Make a restore point and if anythign happens you can go back through a similiar process and restore it back to this time to fix the problem.  That's just some general help. But I think your video card driver is here:
http://ati.amd.com/support/driver.html
go there and then click on:

Windows Vista     
32-Bit Edition        =>     Integrated/Motherboard     =>     Radeon X1200

Install this driver and see if it works after that.