Even though this is an old history - now and again you encounter this problem: Installing the SQL developer edition when already having installed the Express edition coming with VS 2005/2008.
The key to success when prompted with failure to install Client- and Development tools is to run the setup.exe from the command prompt instead of from the GUI; and to use the parameter SKUUPGRADE=1.
- Open a cmd prompt
- Find the CD-drive containing your SQL Server setup files
- Enter appropriate directory (x86?)
- Enter Servers directory
- Type setup.exe SKUUPGRADE=1
The installation process will continue without problems then...