Basically you cant do what you want to do. Fax is old analogue technology. ADSL is new digital technology. The two are incompatible.
So you are left with 2 options:
1. If you have a physical fax machine plug it into the same place where you would normally plug your landline phone into. If you have fax software on your PC, you need to use an old fashioned 56K dial up modem (the ones where you hear it dialling up and making lots of beeping/screeching noises).
2. Use a service like http://www.efax.co.uk/
I cant vouch for efax...I'm just using it as an example of these types of services. There are many others like them on the web.