Hi Claire
Unfortunately, it's almost impossible to guarantee if broadband will be available before you move into a property as it may well be an adsl enabled area, but there may not be any ports free at the RIM or exchange and finding that out before you move in is nigh on impossible.
We were in the exactly the same position as you, we predominantly work from home so broadband is/was essential. Doing the initial online check before we moved in suggested adsl was available in the area. Once we moved in and ordered adsl - no go - no ports available:arghh:
So we had no choice but to order ISDN (64k) :cry:. Fortunately, when the Telstra engineer came to install ISDN, we were talking to him about the problem so he drove up to the exchange to have a look - when he got back, he told us that there in fact was 1 port free, but Telstra hold them for 6 months after the previous owner has finished with it.

So we promptly cancelled the ISDN order and reordered ADSL which was rejected - no ports free. Throughout all this, I'd been kicking up a fuss - I wrote to my local councilor, my state MP (who was also state minister for communications) and my federal MP, then I got the fax number for the then head of Telstra - Sol Trujillo and began 'corresponding' with his office along the lines of essential for business, etc etc.

Anyway, I kept re-ordering ADSL and the order kept getting cancelled until at some point, Telstra decided enough was enough, relented and let me have the available ADSL port :biglaugh:

If you can find a telephone number for a house in the area you're interested in, try checking it on Telstra's wholesale site - http://telstrawholesale.com/tools/adsl-availability.cfm which I believe is more accurate than the standard broadband availability check.

Worse case scenario, would be that you'd have to go with wireless broadband. This isn't as bad as it seems if you really liked an area and adsl wasn't available. The cost of wireless has come down a lot from when we were looking. 12gb per month on wireless is priced from $69 per month, yes it's more expensive than adsl, but the speed is good, you can get routers to share the wireless broadband around the house and at the end of the day, it's a business expense, so although it;s more, it's tax deductible.