Originally Posted by barba
Sounds like a fun project. I am a big fan of rehabbing other folks' cast offs. Getting the crank on the other bike is just a hex wrench job. The only other danger is that the BB spindles will be different lengths or standards. It ought to be close enough, though. If the BB on the Hard Rock is still smooth, you might consider taking it as well. You need a cheap tool and a big wrench.
This may be a long shot depending on where you are, but is there a bike co-op anywhere near you? They are great places to use specialized bike tools for free (plus they often have treasure troves of old parts laying around).
Or, if you're in college or grad school, your university may have a bike shop filled with tools that you can go use for free. Mine does
(university of Maryland)