Quote - You could consider changing your frame rate and then restretch the file to the desired frame rate. Let's say that currently you have one second of animation, but you want it to take 1/2 second.  Render the movie at 15 frames per second and then in a video editor, retime the clip to double-speed on a 30 frame per second timeline.  

It's a kludge work-around, but it should do what you're looking for.

 - Dex

It would work, but you would have rough motion. Your frames would jump from one position to another at a rate that you could see and it would look bad. Even using high-end re-timing plug-ins in, say, After Effects would end up being choppy.

Do the "Select all the keys you want to time shrink, and hold down the CTRL key as you drag" suggestion. This will move the keys selected at a different rate then you drag, proportionally shrinking as you go, (or growing if you drag in the other direction.) 
You may need to drag them a few times to find the right timing, but it will do the job. I've used it a couple times to correct for timing errors in my animations.
I also suggest putting a temp keyframe in a un-used objects timeline. If you place it where you want your animation to actually end, and don't select it with the others, you can drag the other keyframes to line up with it and lock to it. (If you click on the button in te timeline editor for "Lock-to")

Hope this helps!! :D