|First, make note to self to not buy anything with a SiS chipset in the future. They're messy and slow.|
To install the USB driver or any other troublesome device driver, try the easiest route first:
Click on the yellow question-mark and then on Update Driver. Make sure you're connected to the Internet. The system will go to some mysterious location on the net and attempt to pair your hardware with the appropriate driver. Sometimes it will work, sometimes it won't.
If it doesn't work, look for the VEN_ (vendor) and DEV_ (device) values for your troublesome piece of hardware. They'll look something like:
But the numbers for your particular hardware will differ.
Type the vendor data into your search engine. The above vendor code is for Creative. When you know what vendor has made your hardware, go there. Do not go to all those Driverguide type places, they're a pest.
Search on the vendor's support and download pages for drivers for your particular device. In your case it is SiS.
SiS may or may not provide USB drivers for your hardware. Sometimes the hardware vendors buy drivers from other companies and may be restricted to only provide them on the accompanying CDs that come with the motherboard.
Alternatively, you can go to the motherboard manufacturer's home page, like you've already done, and search for drivers for your particular motherboard.
Now make another note to self to not buy stuff from Asus. They appear to have no trouble taking your money for their products, but they seem to be out of money for buying enough Internet capacity for their support servers? Maybe it is because they've spent their money on making fancy but totally unneccessary Flash and Java tricks just so you can choose what drivers you want? Ever heard of folders, Asus?
Never accept to install idiotic "download managers" like the one on Asus' site, to just download a couple of hardware drivers. You don't know what that download manager does behind your back.
Finally. After having found the right driver and verified that it works properly, save that driver along with some short note telling what it is. Like "USB driver for SiS on XP". Stuff disappear on the net and saving the file will save you the trouble next time the occasion arises.