Comprehensive beginner's virtualenv tutorial?

I've been hearing the buzz about virtualenv lately, and I'm interested. But all I've heard is a smattering of praise, and don't have a clear understanding of what it is or how to use it. I'm looking for (ideally) a follow-along tutorial that can take me from Windows or Linux with no Python on it, and explain every step of (in no particular order): - what I should do to be able to start using `virtualenv` - specific reasons why using `virtualenv` is a good idea - situations where I can/can't use `virtualenv` - situations where I should/shouldn't use `virtualenv` And step through (comprehensively) a couple sample situations of the should+can variety. So what are some good tutorials to cover this stuff? Or if you have the time and interest, perhaps you can answer a few of those questions here. Either in your answer, or as a link to tutorials that answer it, these are the things I'd like to know.