Wow, again, thanks for all the support. It's a series ... maybe. We find out the ratings this Friday, and we'll know next week.
I actually got into writing through stand-up, so I had an agent from my abortive acting career. I then started writing, got a job staffing TV shows, and have been working in features for the last 3 years.
If you really want to get started, TV's almost impossible without living in LA, but it can be done. Your best bet is to pick up some books on screenwriting like Syd Field's SCREENPLAY and my favorite Lew Hunter's SCREENWRITING 434 for feature stuff, and then write your movies. Your movies will suck. The first ones always do. Then, after you throw them out, right two good ones, and start calling agents.
For TV, tape a whackload of your favorite show, watch, break it down with a stopwatch, see how the story's done, what characters are focused on when, and then write a script with your own story.
Then do it again for a different show. And make sure both are popular shows. These are your spec scripts, which you then send to agents.
You can also try to find the number for the main office of the a show you want to write on, find out their submission rules, and then try to get in to pitch story ideas. That is somewhat less of a longshot than being struck by lightning ... four or five times.
All in all, the best advice I can give is William Goldman's: "If you want to be a writer ... go lie down in a dark room with a cold towel across your forehead until the feeling passes."