Seen via The Eternal Golden Braid : How to Time Travel for beginners. Unfortunately, because it's a seriously scientific site, you have to start out with a torroidal (doughnut-shaped) rotating black hole the mass of a reasonable-sized star. Tricky, that.
Then there are the problems regarding Hawking Radiation and so on. Though if you can collapse a star to order, I imagine they'd be relatively minor.
Sub-pages contain details about Lorentz Transformations and Dirac's Negative Mass Energy that are about as simple and well-explained as it's possible for them to be. A lot of hard work went into making this subject as easy to understand as possible - which may not be much to those without a degree in Physics, I'm afraid.
Oh yes, when anywhere near a Black Hole, don't forget your Life Preserver.