It shouldn't make any difference to your ISP what OS you have, so why not just use whatever your favorite is? I connect to the exact same phone number with Linux or Windows... er I used to when I could still connect with Linux. No ppp and some boot troubles after my "upgrade"... but that's for another thread when I get around to it.
The only thing that matters in my experience is that you have a true modem rather than a Winmodem.
Yup it doesnt matter of your OS, it depends on their method of authentication and the hardware for your machine. If you already have a compatible modem then you will need to see what type of connections your software supports. then plug in the details from your new isp that met the requirements which most should.
The OS may be crippled by not having the software to support the connection methods/authentication scheme but third party software should be available. My favorite site is Freshmeat.net for Unix apps.
I guess coming from a mac background, I am looking for an installer of some sort, but I am finding that the linux route is usually to edit a configuration file. This is quite cool as the configuration files actually make sense, unlike the gibberish found in windoze.
I already upgraded the ram and changed the grub.conf to show the change..wow..kinda geeky, but it worked.
I'm staying in the KDE environment for now, which is a very elegant interface, my teenagers' friends are coming over asking me to put it on their machines..so it must be pretty "phat".