Just make sure to install each version of CodeWarrior into its own directory. That is:
C:\Program Files\Freescale\CodeWarrior 7.3\
C:\Program Files\Freescale\CodeWarrior 8.2\
Then, as jag pointed out, you're going to have a minor conflict where the last CodeWarrior install (say, 8.2) modifies the registry where when you click on a source file for a CW 7.3 program, Windows is going to launch CW 8.2. A short cut to each CodeWarrior IDE file for each works fine for avoiding that problem.
---Tom