Exactly right: I think home PC's are crossing the gap from merely being a workstaton into a piece of entertainment furniture. That said, I love playing music, looking at boobie pictures, and playing games on my comp.
On-topic: Buy a PS2. As a casual gamer, you have a ginormous variety of games to choose from. Halo is not the only FPS out there, there are tons of good ones for the PS2. Plus, the games you buy now for PS2 you'll be able to play on the PS3. Graphics, console-specific games, meh. These type of things can be easily overlooked for the sheer variety of games available for the PS2. As Ben/Starsky said: Do it. Do it. DO IT.