I have come to the conclusion that it is not a driver issue.
HP have sent me a service pack for the VIA chipset which drives the PCI and AGP slots. This has at least allowed the wireless card to be fully installed and configured.
However, once the card has connected OK, about 1-2 minutes later the PC freezes.
This is the same for each of the 3 PCI slots.
I think I will attempt to swap the PCI card for the USB.0 version. That I am certain will circumvent the issue.