As far as I remember, you can't import 3d meshes directly into AE (as far as I'm aware) but there are 3d cameras with basic 3d elements such as particles and planes that you can use, its mainly a compositor so its not what its ment to do.
The only software I know about that will let you import 3D models directly into after effects is Zaxwerks Invigirator PRO (www.zaxwerks.com). the standard version won't let you do this.
Actually an awesome piece of software the PRO version!
You can upgrade your 3D invigirator that shipped with Production Studio for $199 to the pro version to use in CS3.