As Microsoft's Games for Windows Live service retired, many titles that utilized it have become dormant for online multiplayer. Thankfully many companies are still supporting their games and going back and retrofitting Steamworks (Steam) support into them. Capcom is the latest to do this with three of their titles.
Resident Evil 5, which was always an excellent co-op game, along with Dead Rising 2 and Dead Rising Off the Record are the first titles being transition to Steamworks for online co-op play, achievements, and leaderboards. Right now that's all slated to happen by early next year, so you'll have to wait a bit longer to get your hands on it, but rest assured, your games will continue to work when the time comes!
It's really great to see companies doing this instead of the typical - "our servers are retiring" type schtick we've seen far too often.