<<When I install the software and reboot...>>
i take it you are installing the drivers? What is the source of the drivers? You sure you have the XP drivers?
<<The drivers indicate properly installed in Add/Remove Programs.>>
The proper vehicle for determining (somewhat) the status of device drivers...is Device Manager, not Add/Remove Programs.
Start/Run...type devmgmt.msc and hit Enter.
If you see any yellow or red markings...something needs attention.
Did you disable the onboard video in the BIOS, if applicable...before trying to install the new card?
If I'm interpreting correctly...that card requires DirectX 10, while XP only supports 9c, according to Microsoft. DirectX 10 (per MS) begins with Vista.
What motherboard are you attempting this install on?