http://www.chess.com/forum/view/chess-openings/italian-game-question
Italian Game...response to 2 Knights Defense?

trigs...
that thread is sorta related...though a couple moves down the road.
I am really wanting to know, why not d3? What's so great about d4?

You have to play 4.Ng5 to get the Two Knights. 4.d4 can transpose into the Scotch Opening - probably other openings too. I don't think there is necessarily anything wrong with 4.d3. Maybe you can find this move order in some Itallian Game literature. If Black plays 4. ...d6 after 4.d4, its a Philidor. Happy hunting!

I was wrong. 4. d4 is the Two Knights. 4. ...Ng5 is the main line. Nick de Firmian gives an " = " after 4. d3 Bc5 5. O-O O-O 6. c3 Bb6 7. b4 d6 8. a4 a6 9. Be3 Bxe3 10. fxe3 d5 11.exd5 Nxd5.
For those who like quick attacks, the continuation is 4.d4 exd4 5. e5 and now d5 for Black. Black must be a little bit careful, but he is OK. The line 4. d3 is more positional. White will play c3, castle, and he will open the center with d4 only when he is ready. 4. d3 gives similar positions to the d3 Ruy Lopez. White maintains a slight initiative but Black's game is easy to play.

There is also the Max Lange where white follows d4, exd4 with 0-0. Here's a sampler http://www.kenilworthchessclub.org/games/java/summer05/horowitz-lange.htm
It's a trappy line, but usually it is white that is setting the traps.

For those who like quick attacks, the continuation is 4.d4 exd4 5. e5 and now d5 for Black. Black must be a little bit careful, but he is OK. The line 4. d3 is more positional. White will play c3, castle, and he will open the center with d4 only when he is ready. 4. d3 gives similar positions to the d3 Ruy Lopez. White maintains a slight initiative but Black's game is easy to play.
thank you. that sounds fun...though is it better for White to take the knight or to move the Bishop? I assume the latter?

There is also the Max Lange where white follows d4, exd4 with 0-0. Here's a sampler http://www.kenilworthchessclub.org/games/java/summer05/horowitz-lange.htm
It's a trappy line, but usually it is white that is setting the traps.
Yeah...kind of want something where White wins... But I like most lines that castle early. I like it. I need to figure out exactly how to handle people who take the pawn on e4...at my level - some will.
Well, you want both safe for you and dangerous for your opponent :) I want to be smart, beautiful and rich too...
1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6 4. d4 exd4 5. e5
I don't play this as White, so I don't know how to attack after 5...Ng4 or 5...Ne4. I encountered this many times as Black, were I played 5...d5. The critical line is 6.Bb5 Ne4 7. Nxd4 Bd7. But Black can stir up things with 7...Bc5. There are many complications...
My experience: against lower-rated opponents (<2000), I play 1. e4 e5 2. Nf3 Nc6 3. Bc4. If 3...Nf6 I play 4. Ng5, two knights. If 3...Bc5 I play 4. b4, Evans Gambit. Against stronger opponents I play 3. Bc5, going to Spanish. 3...a6 4.Ba4 Nf6. Here, in order to avoid some Berlin stuff (5.0-0 Nxe4), I play 5. d3, castle, develop and only then break in the center with d4.
On the database I use, I see that White's most popular response is d3. Yet, I see that d4 looks like it is the better move...yet, I can't see the clever continuation for d4...