I had a client whose Outlook 2007 would hang on the splash screen every time he started it up. However, when started in safe mode, it would open up just fine.
After disabling all obvious add-ins, the problem still occurred.
So, some poking around on Da Net lead to some postings that pointed at the Windows Search service. So, I tried disabling that service, and Outlook opened just fine.
A quick trip into the Control Panel to reset the index, a restart of the service (and the machine), and all was good in the hood!