According to this Ecto-Web post, the PC version of Ghostbusters doesn’t have any kind of multiplayer feature, despite online play being present in both the PS3 and 360 versions.
The PC version doesn’t have any DLC listed as a feature, either.
Why? Unknown. We can ask, though.
It’s out on Friday for PS3 and PSP in Europe. If you want it on 360, you’ll need to get the US version. Same if you want it on PC. Thanks, Blue.