Originally Posted by Camilo

So you're talking about the crank arm, not the crank spindle? And what got messed up is the pedal threads on one of the arms?

Something to try before giving up on that arm: take the correct pedal for whatever arm is involved and very carefully begin to thread it in, correct rotation for that arm, from the back side. If you can get it started from the back side - and are sure it's starting to thread in and not cross-threaded, then you might be able to repair the threads by threading it in all the way. Sometimes the threads are only messed up partially, and this will work. The threads in the crank arm are relatively soft aluminum, while the threads on the pedal are steel. They will cut the aluminum threads (which is how they get messed up if incorrectly installed) and can also "chase" (clean up, repair) the threads if the damage isn't total.

You could also check into enlarging the hole in the crank arm and installing threaded inserts - "helicoil" type things.