I played the demo and thought this game sucked. But at one point in my life I considered getting it for online play, why is beyond me. But then I played it, and was disapointed.
Still, why the hell wouldn't you delay the game? Does Eidos really think they'll make gamers happy by not delaying it? NO! Once they're finished it'll just be "I wish it had online play." Finish the ****ing game, don't give us half-assed unfinished crap.
As for Xbox over the net, you basically install a program on your computer, double click the game to join, and they it pops up like it's a game on your LAN. Pretty neat, doesn't always work to well though, and is not the best service. It's kinda like better than nothing, but not by much
And Xbox doesn't have a modem built into it, it has an ethernet adapter. And yes it helps, because it can be easily networked with your PC, thus allowing you to use the tunneling software. But this was really done by accident, MS doesn't exactly want you playing that way. Then they would lose money with Xbox Live. Kinda like how Sony would lose money if everyone used a USB modem and didn't buy a network adapter.