Pacbell DSL disconnecting

ok my friend is running into a problem with his pacbell dsl service where it will disconnect after every 30 mins or so.
you could be playing a game on the net or just web browsing it doesnt matter, it will disconnect.

he has tried switching modems, ethernet cables, different computers and he still has the same problem.

the dsl company came out and checked his line and they said everything was fine, of course his luck, it didnt disconnect when they were there. he is running XP on both machines... he is not running a router currently..

does anyone have any idea how to fix this problem?