Are you having troubles with the installation of xcode 4, because it hangs around 95%?
There is an easy solution for the issue, you just have to open the package contents of the installation, look inside Resources, and execute Xcode and iOS SDK.mpkg
This will bring an installation application (the classic one) that will install xcode without any troubles.
On step 1, you go into you Applications, and look for the XCode Installation Package.
On step 2, right click on it, and press on “Show Package Content”.
On step 3, double click on “Xcode and iOS SDK.mpkg”.
And finally follow the installation steps to finish the installation