A number of people have been experiencing a problem launching the Business Intelligence Developer's Studio after installing SQL Server 2005 Express Edition Toolkit. The problem is that the shortcut is pointing to a file named devenv.exe that isn't there.
Redirect the BIDS shortcut to the location where devenv.exe actually exists.
You should be able to successfully launch BIDS now.
Note: When you launch a shortcut to a file that is missing, Windows will try to find a matching file somewhere else on the computer. When I was testing this issue, Windows XP actually found devenv.exe and offered to fix the link for me. I clicked OK, the shortcut was fixed and BIDS launched. I guess it pays to be patient (or distracted).
This happens when you have installed any Edition of Visual Studio 2005 into a non-default location onto you computer prior to installing BIDS. BIDS makes some (bad) assumptions about where the VS development environment is located so when you install VS to a non-default location the BIDS shortcut is actually pointing to the default location for VS installations.
This all happens because BIDS is really just a set of Project Templates that install into the normal Visual Studio environment (devenv.exe).