Even though the underlying ColladaModel class imports not only diffuse texture maps, but also specular maps, environment maps, normal maps and opacity maps, only simple diffuse texture maps are converted to the XNA content model within the pipeline extension right now.
Therefore conversion of these texture maps to the XNA content model has to be implemented (I personally don't know how to do that right now).
Texture maps are now generically added to the OpaqueData dictionaries of both MeshContent and MaterialContent nodes. This is compatible to the Normal Mapping sample from App Hub.
Even though the underlying ColladaModel class imports not only diffuse texture maps, but also specular maps, environment maps, normal maps and opacity maps, only simple diffuse texture maps are converted to the XNA content model within the pipeline extension right now.
Therefore conversion of these texture maps to the XNA content model has to be implemented (I personally don't know how to do that right now).