I started a thread over at AVSForums on how to install the ATI HDTV Wonder and a analog TV tuner in a Window XP Media Center Edtion 2005 box.
Basicly, the technique requires you to install the OS and MCE first before physically installing the cards in a PCI slot. After the basic OS install, load up the drivers to the repsective card, shutdown, physically install the card, and restart and let Windows install the drivers.
Now, it seems that you are dealing with a plain vanilla Windows XP, which usually is less problematic, but I'd suggest the same installation technique.
But, before you even consider the HDTV Wonder, I hope you did the proper antenna analysis because if you can't get a good signal from your local HD broadcasts, forget the HDTV Wonder performing. See AntennaWeb.org and CheckHD.com.
If you try to install the HDTV Wonder is a box that has been around for while, you might be asking for trouble. The better practice is with a new installation of Wiindows. Microsoft Updates has a special "HDTV rollup" for HDTV tuners in addition to the other updates. XP's SP2 is essential.
In brief, new updated Windows XP; install the analog tuners drivers and software, shutdown, physically install the analog card, restart. Check Device Manager.
Install the latest HDTV Wonder drivers and software. Shutdown. Physically install the HDTV Wonder card. Restart. Check Device manager.
Now, you do realize that the HDTV Wonder produces standard analog TV as well as HD in non-WMCE boxes. However, if you're doing a WMCE box, then a separate analog TV tuner is required to properly setup the TV channels.
Except, there are hacked Catalyst drivers from a guy named Kram that will allow you to install a HDTV Wonder in WMCE without having the need to install a separate analog tuner.