You can open the assetbundle and extract all assets with an install of Unity 3.5 (using AssetBundle.LoadAll() and some AssetDatabase functions to save all your assets to your project)
But if you are not in the original project of this asset bundle, you will not be able to recover shaders and scripts from the assetbundle because they are only stored in the compiled project and not in the asset bundle.
Then, if you achieve this step successfully, move the assets to Unity 4.2 and re-compile all the stuff…
Anyway, I don’t think there is an easy way to do this if you don’t have your original 3.5 project and assetbundle sources…