I downloaded the source for 2.4.33 as Paul suggested, compiled and installed and the 'unresolved symbol' error message has gone away.
The wlan module now loads - hooray. End of part 1.
Now the difficult bit - I've got to get a card that works with the Atheros drivers.
The Atheros site lists this as one of two:
AirPlus Xtreme G 108Mbps PCI Adapter DWL-G520 PCI 802.11b/g AR5002G Super G
This is available at the moment for only £20.00 plus carriage at http://www.pixmania.co.uk/uk/uk/92365/art/d-link/dwl-g520-pci-wireless-net.h... The picture on this site matches the label shown on the D-Link site shown as DWL-G520 Revision B
Does anyone have any experience of these? Atheros doesn't mention any revisions so does the Rev. B still have an Atheros chipset?