I'm using Sony Vegas Pro 12 and after I finished recording a video with my webcam(originally 20 Minutes Long)it was 6 Seconds long however, whenever I hover over it, it shows that it was recorded for 20 minutes?
I assume you are using the DV capture utility and just because it works with a USB web cam you think that's supported but it's not. That utility is for capturing DV video from tape via Firewire. It is capturing uncompressed video and uncompressed audio from your web cam via USB. If your web cam is the normal SD 640x480, that would be about 800MB per minute of video+audio. At that data rate, a normal 7200RPM hard drive would be dropping frames and a 20 minute video would be 16GB in size.
You don't want to use Vegas Pro to capture from your web cam. Use some other program that actually does use a codec and doesn't create such large files.