If you have a slow ADSL broadband the first thing to do is eliminate a faulty line coming to the building. The best way to test this is to run a Quite Line Test. This test is not the most scientific and relies on the sensitivity of the human ear. However your ear is very good at picking up noise interference when it is supposed to be dead quiet.
This test pin-points interference between the Exchange and Master socket (the demarcation entry point into the building).