I've recorded a lot of my audio guitar performances successfully, enjoying the ability to edit out some mistakes thru post-production editing of the .aif files. Typically I just plug the guitar into my amp, and plug the amp's line output into the the audio input jack of my Macintosh computer, and record directly into Sound Studio. I'd like to make the jump to doing a video recording, but the problem of how to sync and edit the audio seems more daunting since any edits require precise sync of audio and video. I've got an HD digital camcorder with a 3.5mm external mic input jack. Seems like I'll need to connect the output jack on my guitar, to a small preamp (i've got a SansAmp that might do the trick) to boost the low level signal from the guitar pickup up enough to generate appropriate volume in the video, and also to feed a signal into my headphones so I can hear what is being recorded. Once all this is done, and I have a video, I can run it through IMovie to edit as needed. Am I on the right track?
There are a couple ways you could go about this. If you can do it in a single take, then you can record the audio and video at the same time and then simply sync them up and all will be well in the world.
If you want to be able to do multiple takes, then what you should do is do it the way they make music videos. Do the audio first, make your recording and do your editing and multiple takes. Once you have done that, play back the audio aloud and fake it. You don't actually use the audio from while playing in the video, you just record yourself playing in sync with the pre-recorded audio. After, you do the same sync process as you would have done with the first option.