Many ISP have a 2 hour reset to stop continious use of file sharing apps....You'll have to check the small print of your agreement and see if this applies to you...if so no way round it other than to re-dial each time or swap for a 24/7 access package.
It's the same with Freeserve and a few others. You could always download a file downloading manager such as Flashget, to resume any downloads that were broken as a result of the 2 hour cut off if that was your main concern.(legal downloads of course)