Can Xbox users play against/with PS3 users online?
Example: in Medal of Honor: Airborne?
My assumption is no, because they have to be members of the same Xbox Live or PS3 networks.
But I don’t know the answer, anyone know for sure?

No. They can't.

The only cross platform games I know of are uno, shadow run, and halo2. Pc and 360 can play against each other.

Oh and blizzard has games that mac can play pc.

No console games cross play. Xbl is 50 year, ps3 is free. If you could play your buddies without paying, everyone would just get the ps3.

Halo 2 cross platform??? That is news to me, it seems like it is not true though.

Final fantasy can play x box and ps2 players

I guess it was canceled. But it was mentioned or hinted at.

http://www.gameinformer.com/News/Story/200701/N07.0109.0005.10722.htm

Halo 2 cross platform??? That is news to me, it seems like it is not true though.

I think Halo2 was a big-hitter in the "games for windows" and "windows live" campaign. I knew they were working to integrate Windows Live and Xbox Live but I thought it would be quite a way out.

Since Halo2 was for Xbox (which is x86 with Nvidia graphics) I'd imagine that was easy enough to integrate.

To clarify...

Cross platform between Xbox 360 and PC? Yes, some "Games for Windows" titles do indeed support this feature.

Cross platform between Xbox 360 and PS3? Generally no.

No. They can't.With Final fantasy XI (its own severs) can play xbox360, PS2, PS3 & PC players online