Valve says there is no technical reason why Team Fortress 2 players on the PC running Windows Vista couldn't play with and against Team Fortress 2 players on the Xbox 360.
"We'd love to, technically from our side, there's no reason why we can't," Robin Walker, designer and engineer at Valve, told GameInformer.
"[I]t really comes down to knowing Microsoft has announced that Shadowrun is going to do that, but they haven't let anyone outside of Microsoft, I mean we don't have an API or anything."
Asked whether fan-made modifications for the PC version could conceivably appear on Xbox 360 or PlayStation 3 as downloadable content, Walker said, "From our perspective, we'd like to do it all.
"We'd love to have the Xbox and PC play together, and technically, from our side, there's no technical reason why you can't - the engine is the same, the network they use is the same."
"It really comes down to negotiations with Microsoft," he added.
Cross-platform multiplayer is one of the key elements of Microsoft's (slightly bewildering) "Games for Windows - LIVE" service, due to launch on 18th May, with Shadowrun and UNO likely to be the first games that allow PC players to mingle with and generally kill their Xbox 360 counterparts.
Team Fortress 2 is due out this winter as part of bundles on PC, Xbox 360 and PlayStation 3 - with the latter in development at an EA studio in the UK.