According to Rockstar (via videogamer.com), there will be no demo version of Grand Theft Auto 4, so if you were hoping for a free taste of Liberty City, you're SOL.
"Much of GTA 4 is the driving around and we wouldn't be able to give out the whole city. We would have to give away half the game for free. People would think Liberty City is a tiny city. You run into problems," Rockstar said.
"If there was [going to be a demo] we would have talked about it. With a game like this the guys at Rockstar North will want to spend every minute making the game look great. Most people know the concept of GTA anyway. I don't know that the demo is worth the time and effort."
So basically: Everyone already knows what GTA is about, and, let's face it, we're going to buy it anyway.
Videogamer.com: No GTA 4 demo