Hi Leon,
Not sure how much help I can be but I just bought one of these:
http://www.ebay.com.au/itm/280718273205
to get wifi working on a 13 year old lappy and it worked. It has it's own software so it doesn't use XPs terrible wireless drivers. For only $8.90 delivered, perhaps you could give it a try and see if your lappy or desktop can connect to the Telstra wifi thing.
Hugh