Applications/Xcode vs Developer/Applications/Xcode
You seem to have upgraded your system with older versions of Xcode present on it and missed uninstalling Xcode 4.2 while installing Xcode 4.3.

Xcode from version 4.3 onwards installs under /Applications. Only versions older than this (like your Xcode 4.2) install under /Developer. If you do not plan to boot OS X Lion from another disk/partition and use Xcode 4.2, you can safely uninstall it (do not just delete the folder from Finder).

To uninstall Xcode 4.2:


Open Terminal (Applications->Utilities->Terminal.app)
Type the command sudo /Developer/Library/uninstall-devtools --mode=all


To uninstall your Xcode 3.2.4 under /Developer-3.2.4:


Open Terminal (Applications->Utilities->Terminal.app)
Type the command sudo /Developer-3.2.4/Library/uninstall-devtools --mode=all


Reference:
How to remove Xcode from your Mac