Problems installing SiS 650 Update. Can anyone help?

[Piccolo00]

I'm having trouble installing the SiS 650 update from www.sis.com.
I go into device manager click properties on SiS AGP.
I click update driver and have it look for updates in the folder which has all the files that i downloaded.
BUT
It says that there is nothing to update!
I have never updated it before and my games lag about 30 minutes into the game.
Can anyone help???
System:
Windows XP Home
512MB Ram
2.2GHZ Pentium4
ATI Radeon 9500 Pro
300 watt power supply

If anyone can provide any help on how to install this or if this problem is caused by anything else please let me know.

[Peter M]

Are you trying to install the VGA driver onto the AGP bridge?