To remove the blower motor, you need to remove the glovebox (follow
these steps), then remove the side kick panel (one 10mm bolt/screw and a plastic nut, then it slides out), remove 3 screws holding the blower motor in (you may need to remove one or more of the connectors that are behind the kick panel to access the last screw), then it slides out. As for the actual blower motor housing, I don't know.
You may not need to remove the blower motor housing to find the grommet, maybe even just removing the glove box (if you haven't already) will help you find it. I've never ran wires to my doors so I don't know its exact location.
A little off-topic, but does your blower motor make a light ticking noise if it's at setting 1 or 2 (assuming you have manual A/C controls), like in this video?
[youtube]
http://www.youtube.com/watch?v=ts-OoRFLSrw[/youtube]
If it does, and you're annoyed by it, there is a cover you can purchase to quiet it down. Read
this thread.