Depending on the system, some rules could be legally available online. Pathfinder and Dungeons and Dragons 3.5 have a System Resource Document available for free online, which would be a big help for you.
But like allworth said, do try to the Players-Wanted thread to see if anyone is playing those systems. Or you could start a thread in the Wanted-GM (Game Master) forum if you're looking for a specific kind of game or Game Master. Some GMs run lower-level games for newbies, or might run you a short solo campaign so you can see what's what, but you may need to ask for it.
You could also see if someone would let you lurk on one of their games. Lurking means you can see everyone's posts, even though you can't post, letting you see a game in action and how posting format and game play work in action.
If you'd like to lurk in a low-level D&D 3.5 Game, you can come over here:
link to another game and hit the "request access" link in the upper right-hand corner and drop me a line.