I ran into this problem trying to use the SQL Server 2008 R2 Business Intelligence Development Studio (BIDS), which uses Visual Studio 2008 Shell (integrated mode). Every time I tried to create a new Integration Services Project, I was getting an error, "... The specified module could not be found. (Exception from HRESULT: 0x8007007E) (System.Windows.Forms) ...".
As other posters have noted, the files in MSDesigners8 seem to be corrupted. I didn't think to install SQL Server 2008 R2 BIDS in a virtual machine to get copies of the DLL's to put into that folder, but I found a solution which seems to work: installing the Visual Studio 2008 Shell (integrated mode) SP1.
Before that, I renamed the MSDesigners8 folder to MSDesigners8_old (and the .dll files were also renamed .dllold. I don't think that matters necessarily; I'm including it here only in case it does matter). I tried repairing as well as reinstalling BIDS, but it did not recreate the MSDesigners8 folder. Installing SP1 did.
After that, it may also take a reinstall of BIDS, but it may not. Good luck!
HarshdeepGupta
has included a blog post link that has some files included. Take a look at his answer. – Ostmark