After Effects can only import 3D objects in PSD files.
So, to get your Google SketchUp 3D objects into AE, you'll need Photoshop Extended.
In Sketchup, go to File > Export > 3D model. Choose Collada (DAE), since that works nicely with Photoshop CS4 Extended (some Sketchup features may be lost in the export, though).
Open the DAE file in Photoshop CS4 Extended and save it as a PSD file.
Import that PSD file into AE as Composition or Composition - Cropped Layers. Make sure you enable the "Live Photoshop 3D" option in the dialog.
Note that this doesn't actually bring 3D geometry into AE and also that these 3D models won't intersect AE's own 3D layers in 3D space.. Instead, it brings a layer that has the 3D model rendered inside ("live") as you move around AE's 3D camera. You can also move the 3D object using a Null object automatically created by AE for that purpose.
More info in the After Effects Help page on 3D object layers from Photoshop.