I filmed a small wedding this past weekend using a HV10 (SD mode). It was more like a favor than a job. The reception was held in a small room with very little space to move. I was practically forced to face a window with light coming through it. Not only that, one of the walls had a big long mirror on it so light was bouncing off of it right into my lens. So now, some of the footage is obviously dark. WHAT, if anything can I do in post production to brighten these parts of the video or make it viewable? I won't be using everything I shot in the final edit but some of that is vital! I have iMovie HD and iMovie 08 at my disposal. Would i need anything else?

You're kinda hosed, but you might be able to save it in post. If you have any sort of color correction in i-movie you can drag down the input white value which will brighten it up. You'll need to tweak the gamma a bit and probably boost the color saturation. The down side is that the picture could end up looking a bit artificial or slightly "off". If there's any way you can work in a 10 bit color space you might have better luck but I think your options are limited with the tools you have.

Since it sounds like you shot everything from the same location, you might want to take a scene and play with it to see what you get. There's no real magic bullet solution for you in this one.