ADSL performance is predicated on a number of factors. Of primary importance to the potential speed of ADSL is the distance of your house from your local Telephone Exchange.

Using Google maps you can roughly calculate your distance from the exchange:

1. You need to know your home address. If you don't know your address seek help! No seriously.
2. Discover the location of your Local Telephone Exchange
3. go to google maps for your country e.g. http://maps.google.com.au
4. Click the Get Directions link and enter your home address and the exchange address. Then click the "Get Directions" button

You should see something like this. The distance will be on the left. I have highlighted it in yellow.

This is a guestimate only. Telephone cabling generally follows the local roads. However the Telephone cable could take a different path from the one google maps autopicks. But it's enough to get a rough idea.