Maya 6 has incorporated normal map generation, but unfortunately, it's not quite as robust as I'd like.
Turn on the TransferSurfaceInfo.mll plug-in in the Plug-In Manager and it'll be under the Rendering menues, Lighting/Shading > Transfer Surface Information > Options.
You'll want to select the lowpoly model first and shift select the high poly before activating the command.
Now, this just generates the normal map. In order to actually display the results, I believe you'd have to make use of some sort of plug-in like Nvidia's CgFx plug-in.