I'm no expert but I think most web cams are of very low quality.
I bought a digital camera for about $100 and it's compressed, pixelated and jumpy.
What I ended up having to do was get an A/V input card for my computer off eBay. (audio/video in), then use my old Hitachi 8mm Camcord. (VM-E625LA)
You set it to pause and leave the tape door open so that the camcord doesn't shut off automatically after 5 minutes. Then use Adobe Premiere to record and edit. (I tried a couple of shareware programs and they were really buggy) When you set it up to record you can do it at the frame rate and quality that you want and you can monitor it either from the camcorders built in screen or the computer monitor.
For the audio input I use the output from my mixer, so I can record both guitar and voice using better equipment than the camcorder has.
When you're finished you have to convert the finished file to .flv format which reduces the quality depending on how much you have to reduce it.
The only problem with this kinda setup is you can't use audio software like Cubase and run Adobe Premiere at the same time. So if you want to give a lesson with backup music, you need a second computer. (either that or record the music and guitar part ahead of time, mime the actions later on video and sync it up manually... which is a major pain)