Xcode refuses to launch after first launch.

Hi, I am relatively new to Macs and am looking to program for the Iphone, Ipod and Ipad product. I downloaded Xcode from the apple developers website and tried to launch it, and it wouldn't work because my software wasn't up to date. So i updated (to 10.6.4) and reinstalled. The program ran ONCE and than gave me the same error message as before upon opening (try updating your system software, make sure you have the newest version of Xcode, and/or reinstall the program). At this point I have reinstalled the program numerous times trying different things and it still won't work. I went to the OS X Cd that came with my MacBook Pro and ran it, installed Xcode from there (which is only 3.1 unlike the Xcode on the developers website which is 3.2.3). That version of Xcode launched multiple times with no problems and I was even able to write basic programs into it. Eventually though i closed the laptop and went to sleep, woke up this morning and tried to open Xcode and it gave me the same error message i was getting before. Any suggestions on how to fix this?
MacBook Pro-
2.8 Ghz Intel Core 2 Duo Processor, Version: 10.6.4, 500GB storage space.

I would try uninstalling again and rebooting before re-installing. I'd also use the version from Apples site. To uninstall, there is a command line tool. I believe it is mentioned in the readme notes.

Also open the Console.app in the Utilities folder and check for any extra messages that may give some extra clues.

The uninstaller is in /Developer/Library/ and is called uninstall-devtools. Run that from the CLI. See here.