a HOW-TO for the hitherto unbeknownst to most, and furthermore handy-as-phuck 'Audio-for-YouTube Video Capture & Merge' technique:

It's easy; 1st you need a few hours to kill. And a worthy subject :D
Also a soundcard with inputs and some free software - even a cheapo Soundblaster gets a much better result than a camera's built-in mic. The key is to 'go direct' with good signal/noise, and of course avoid ground hum like sweaty nuts in the Arizona summer. (ed-If you already know about preamps and sound recording and such then you already know how to do this stuff and should bugger the bloody hell off, Professor Dork-ballness).

As to the procedure:
Record the video normally however you like, while at the same time run the output of the instrument or mic into a mixer or DI and then send it to the soundcard... or if your card has preamps you can go direct w/out a mixer. I also use audio tracking/editing software such as Reaper or CoolEdit to capture and prepare the audio. You don't need to buy an editor, or even use one. You can just dump the .wav into MovieMaker as is - 'raw'. Or download a free audio editor.
Once it's recorded, be sure the audio file is saved as a .wav for high fidelity. Avoid any use of mp3 compression. Save your video file seperately, of course.
Next, I use video editing software (MovieMaker 2 on PC or iMovie on a Mac) to combine. Simply import the audio file and video file, then line them up on the timeline so they are synced - I do it in MovieMaker by adjusting the blend of video sound w/ the audio file sound.
Once the audio & video are synced I add text, and then video effects. Save the project often. To export/output the new video file for YouTube, in MovieMaker go to File->Save Movie File... I use the setting "high quality video (small)": 240x320 resolution@30 frames/sec and end up with a good picture compressed to about 1 MB/minute. Upload the new file to YouTube and that's that.

other stuff:

currently working on a sound+vision adventure called Mankind_OOPS!
...or something of this nature. The reality of the project has yet to bear its final fruit. It is still pending mastering and final artwork, Dual-disc animation, web-kiosking blah blah

A Wrong Turn remains in progress. The end of production for this sorry little feature remains to be seen.