Yes, the blue pair can be used. If all you have is Cat-5e in the house, and every jack is hooked up with the blue pair, you are set to go. Now on the catch-22, if they did not home run everything back to the basement, you would have to place filters on every jack, if you have just regular adsl. You can still find the Secor/Corning ADSL filters that go in the NIDS, but those are going away, due to providers moving over to dry loop, or such as how U-Verse from ATT is, that you no longer need filters.
I just took all of my lines, when I rewired the house, when we first moved in, into a unit that I got from Radioshack, that was for telephone wiring. All that you really need, is either a punch-down, or use a terminal block to connect the blue pairs to, to help clean that up.
For the DSL line though, try an existing jack, after you get the mess cleaned up, to see if you do not have to pull new telephone wiring.