I'm not a gearhead, but having experienced an almost identical problem a few years ago in my mom's 90 Honda Accord LX 5spd, I think it's probably one of two things:
1) The transmission has come detached from the drivetrain; this is what my dad thought was the problem when I called him about it (Mom was out of town), and would have cost more than the car was worth to fix. Fortunately, it turned out to be:
2) The front axle, which had been replaced by- and was still warranty from the Midas I'd had it towed to, so it cost nothing to fix.
The problem was very similar to yours, I'd gotten out of the driveway and to the entrance of our subdivision just fine, but pulling out onto the highway the car launched and then suddenly I was getting no power at all. I pulled off immediately, waited for some traffic to pass, then tried again. In first gear it would make this grinding sound as I let the clutch out; similar results in second, but I found the higher the gear I was in the heavier the grinding sound. Releasing the clutch in 1st or 2nd did *not* kill the engine, but it would in third, fourth, fifth, and reverse.
Needless to say, when my dad got home the following evening and I told him it would cost nothing to fix, he was pretty damn happy.
--T.J.
...)