Useful newbie go player resources:

The Way To Go (courtesy the American Go Association) is the hands-down best introduction to basic concepts in the game.
Once you've got the basics down, Sensei's Library, GoBase.org and goproblems.com are all excellent resources.

For computer go (as in, versus a computer opponent), you can find GnuGo and various interfaces for it. For a human opponent, look into IGS and KGS. There's also Yahoo Go, but it's a bit less of an interesting and meaningful environment than IGS/KGS are.

The official IGS client, GlGo, also functions as a GnuGo interface, making it doubly useful. It's a must-have app.

You may have a local go club or association in your area... but that'll probably require some more resourcefulness to find, depending on where you are. Internet Go is all well and good, but there's a certain quality to actually sitting across from your opponent that's generally more appealing and motivating in the long run, I think.