PCNCI Cards

The wireless you have in your laptop to connect at home is not wireless broadband.

So you can not just buy a prepaid card from Telstra.

What you locked on to was someones wireless access point like you have at home and they have not changed the name from the default name.

Cheers
Ross

More probably it locked onto a Telstra public wifi hotspot. It will say Telstra CBD, or similar.
When you get on this, you need to open your web browser, which will allow you various payment options. It isn't cheap, either.
My recommendation would be to find a cafe with free wifi.
Cheers,
Tim

I have Bigpond wi-fi at home like you. I used a PCMCIA card on my old lap top but they have had it built in to lap tops for the last couple of years. The network your computer found was like the one you and I have at home which is secured.
Some folks have unsecured wi-fi networks in their homes and are not aware they are open for others to use.
There are also free wi-fi networks in many caravan parks etc. Then there are bigpond's own wi-fi hotspots you pay to use. There is a list here...

http://www.telstra.com.au/wirelesshotspots/locations.htm

You need to register, then download the software from the email they send you.