2 fibre optic lines running into the house?? God knows what they were used for, BT private circuits perhaps but unlikely. ADSL uses your normal phone line, however it only uses the higher frequencies not used to conversation hence you can talk on the phone whilst netting, but an ADSL specific modem is required. If you need speed ADSL/Cable is your friend....
Personally I've got an ISDN connection running into my room but the company who ran it went out of business a long time ago hence its useless, I would be intrigued to find out what the optics were used for though, hell of a lot of bandwidth there.