Do the usual maintenance on your dad's machine, delete temp files ... defrag ... and run other programs that will hunt for trojans, adwares ... etc ...
And lay off the downloads when your dad's online ... that should help too ...
there is a very simple solution that has already been mentioned. why don't you connect his box directly to the intarweb, leaving your machine out of the equation? if it's shit AOL's fault, then he can't put you to blame. if it's suddenly fast, guess whose fault it is?
i tried using P2P apps on a dedicated box at my parents place. i dl very little because i am really only looking for a few specific things, and i was mostly "in queue." the shit still brought the network to it's knees though mostly due to what others have noted about upload bandwidth.
after about 3 days i shut my P2P box down because unlike you i'm polite. my dad never directly asked me too stop, but he mentioned (as i had already noticed) that the network was hellaslow. i move into my new condo in a week and once i'm paying for the connection i can download whatever the hell i want. till then . . . .
Hey folks, if you want to run p2p stuff on a multi-user network, and you don't want to hinder other people's connection, you might want to look at a linux firewall/router setup. With the later kernels, you can do some fancy packet shaping that would give your filesharing packets low priority over the network, so everyone else would be uneffected by your stuff.
Just a thought. And no, i still don't quite understand how to do that, but you folks are smart, I'm sure you could figure it out if I gave you a link: http://lartc.org/howto/