ODST Question

Okay, so I've been thinking of buying Halo ODST sometime soon. I know that it's a two-disc game, with Disc One being the new campaign and Disc Two being the "complete Halo 3 multiplayer experience". But is it possible to play online with people who have the original Halo 3 disc when you have the ODST disc? I'm wondering this because I don't know very many people that have ODST personally, but I do know a lot of people who still have Halo 3. Please forgive me if that's a stupid question, because I just got my 360 yesterday.

if you use the halo 3 multi-player disk you can play online with people who have the original halo 3 disk

Yes, you can play with them. The multiplayer disc is pretty much considered Halo 3 for your achievements and such.

You wont be able to play the new mythic maps with them though.