LinuxQuestions.org - Explaining "mem" & processor usage??

I've read the man pages, I'd still like to know more about what I'm actually seeing.

When runing mem, free, or top...

Where can I get a much more in-depth explanation of what I'm seeing?

Memory:
Available, Used, and Free are self explanitory. But what is shared and buffered? Swap has no shared listing, but it does have a cached listing, which does not equal the used listing. What is all this sharing, buffering, and caching all about?

CPU stats:
Why is load average always so low? 0.05, 0.10, ect. I've seen it as high as about 3% but that's it, even on a system running a very heavily loaded database. Does this really mean I could theoretically throw another 80% more threads at the CPU and it would run them without a slowing? (limits of system bus and Ram aside)

And finally... what the heck is a "zombie" process? What's a "nice" process? Are there "mean" processes also? :D

I know this is super beginner stuff. I've been doing L* stuff for about a year now and never really paid too much attention to this, but I want to tune these network servers better and need to better understand this stuff.

Thanks!!