It does sound more like a dns problem... But - doing the Repair thingy, switching off modem, restarting pc, working some voodoo magic etc won't do any harm, so it may as well be tried.
rach, maybe just telewest having sum sorta probs then. its jus one of them things really ur probs jus gonna av to bear with till it sorts itself. try all of the above suggestions tho, as mike says, cant do any harm