I use mninter.net at home on 56k modem, works great.
(the new infinetivity web site needs work from some
real web designers, right now it has big klunky
gifs, frames, flash, yuck!).  My chat script logs in my
username and password before invoking pppd.
I suppose the auto-chap/pap windows stuff should also work..

I recall dialing in with minicom and seeing ascend
or some other popular routing gear annouce itself.

karl.