IsLame, I just seen the video, and it is great. however, I wish it was a bit louder. The voice is very muffled. I think you might need an external Mic. Maybe your PC mic is defective or your recording settings are not OK. Is your Mic Boost on?
I am sure Hassan has some good advice on how he has a good and clear audio for his videos!
I don't have a PC (I have a Mac) and am no computer expert, but I changed my "Sound" Preferences in the Control Panel - and I'm sure if you do that, IsLame, you will be able to improve sound quality.
OR... as I said before, why not record your voice in another program? I use "Garage Band" and then save it as an mp3 (mp4 actually) and just drag it into iMovie (Movie Maker in your case) and add pictures.
The sound quality on my videos is much better since I started doing that.
