Totalvideogames.com has posted an interview with Bioware's Dr. Ray Muzyka on the upcoming PC version of Mass Effect, going over some of the differences between it and the XBox 360 version, including the DLC:
TVG: Are there any other features of the PC version that will be different from the Xbox 360 game - any other things that have been tweaked?
One of the big changes is the tactical HUD. It allows individual squad command controls, so you can actually tell your party - individually as opposed to a group - where to go. And then you can give them specific individual orders…for what they're going to do when they get there.
Additionally, we've made it so that the main character can do more abilities in order on PC, so they can chain their abilities. And if you put those two things together, you have more control of your squad and main character, so you can enact more interesting strategies…We changed the inventory screen so that it's optimised for PC in the process, so that we've made it even easier to use… Everything is really in tune to the mouse and keyboard..
TVG: The Batarian expansion has already been made available as Xbox 360 DLC. How will PC gamers be able to get hold of that?
Basically, it'll be made available as a free download at launch. It's not in the box, but basically you just download and install it immediately, and it's free for PC fans.
TVG: I'm unaware of exactly how much DLC is available for the Xbox 360 game at the moment…
Right now there's just one pack, but we have plans to do more in future for Xbox 360 and PC. We haven't announced any details on that yet though.