this doesnt exactly fall under the domain of time-travel, per se, but since you mention black holes. there have been theories about traveling great distances through space in short amounts of time by navigating through wormholes, but they generally require the use of matter that as far as we know, doesnt exist. this hypothetical matter would have to be extremely dense and self-repelling, as it would basically be a stint in the torn fabric of space-time. it would have to hold open the wormhole and keep it from collapsing in on itself. travelling through this wormhole would allow ginormous (highly technical astrophysics term... yeah.) distances to be covered almost instantaneously, but it would still be sublight speed.
i found an interesting article here:
http://www.aleph.se/Trans/Tech/Space...wormholes.html that i'm going to have to read more carefully when i have a little extra time to spare... it goes through time-travel, wormholes, all sorts of cool stuff like that.
as for actual time travel and CP's thoughts about traveling back or forward... i think traveling backwards (to any point, not just the creation of the machine itself) is impossible due to the difficulties of paradoxes and all sorts of timeline shifts, would could be cataclysmically devastating - you accidentally kill the great-grandfather of the guy who invented the time machine... poof there goes the machine. go back and risk messing up the timeline. go forward and you're subject to any number of timeline shifts that could occur because of changes in what's happening in your own time. who knows, maybe because you're not in your own time, someone else dies and suddenly the population changes just enough to create a chaotic butterfly effect in the future. stuff happens.
I think i'm revealing too much of my sci-fi fascination/geekiness here. time to be quiet.