I signed up with one outfit that insisted that a call placed to a nearby city was indeed a local call. So, if you live in the country, make sure you check local numbers with your phone company before logging on. In searching for free access, it is best to start with the major search engines - Excite, Alta Vista, etc. It's pretty straightforward. You find a local dial-up number first, then download access software.
Installation can be another matter.
Everybody wants you to make their service, free or not, your default Internet connection. I have a couple of Internet access accounts just in case one's servers go down. So, before you install, write down your current ISP's Internet address, and your user name, password and other settings and put the paper in a safe place. When you install, think about whether or not you want the new ISP to be your default service. If you're fortunate, the install software will respect the integrity of the old ISP settings and just add itself to your Internet setup software.