its very very simple..........I use AOL 6.0 and before i tried this i was disconnected every 15 minutes ! i even went on a mplayer strike and played with the AI for awhile.But then i thought of 3 solutions.
1)If Your ISP has a chatroom option do what i do ,I recommend opening it and then going to play CTP (this prevents thee isp idle timer from given you the boot)-it now kicks me about every 3 hours,Because the people chatting.
2)hit ALT-TAB after each turn and surf the net ( once again to stop idle timer which is set for 10 minutes on AOL,other ISPs timer differ)
3) go get Alta-Vista Free internet Access.There are ways to erase the Ads and the ISP has no timer.My personal expierence with this one is great. I played for almost 5 hours before my modem hung up!
Anyway the reason why most ISP have system timers is simply these reasons .They tell you to prevent Internet traffic but its really to make you dial up more so they get more money
Anyway i am working on a ping device that keeps in touch with the ISP.It may lag you out a bit , but i can tell it will be a MUST if youre an AOL,MSN,or EARTHLINK user cause those have the worst sytem timers.