You can install Xcode in different folders now with 3.1.x.
The 3.1.1 is really meant for iPhone DEV and it totally messes up projects from 3.0 Xcode if you go back and forth on different machines for any reason.
Basically you have to commit to only 3.1 or 3.0 and not mix and match them as it will drive you nuts trying to get projects to build the same on either.
Basically you have to commit to only 3.1 or 3.0 and not mix and match them as it will drive you nuts trying to get projects to build the same on either.
You can set which versions of Xcode the project is meant for in the project settings window. If you switch a lot it is probably best to keep all your projects in Xcode 3.0 mode. But I would still probably use the latest version of Xcode just for the bug fixes.