JohnT - I'm also a newb but I will try my best to help you.

1. How do I umount the 6 gig HD? - Is this Mount or Unmount?

2. Why isnt it showing up in the My Computer thing anymore? - It is not showing because it most probably have the ext3 (linux format)

3. If and when I get it installed to this HD, im not exactly sure how to boot from that HD, would i just do the good old F11 boot menu at startup and choose my second HD? - When you're installing, you'll have the option of dual booting (if you have windows)
4. Once on knoppix will I still be able to access files from my other HD (Like my music etc) and same vice versa.... - you have to mount the other harddisk (windows) once you've installed/run Linux

5. There is no 5, thanks in advance though to ANYONE who can help me out! - You're welcome.