Package 'Visual Studio Common IDE Package' has failed to load properly...

I get the following message from Microsoft Visual Studio 2008 Standard SP1 whenever I try to open a web solution.
Package Load Failure
Package 'Visual Studio Common IDE Package' has failed to load properly ( GUID = {6E87CFAD-6C05-4ADF-9CD7-3B7943875B7C"} ). Please contact package vendor for assistance.  Application restart is recommended, due to possible environment corruption.  Would you like to disable loading this package in the future? You may use 'devenv /restskippkgs' to re-enable package loading.

This started a few days ago.  I tried to load a backed up (known good) solution, but got the same results.
I have tried everything from completely re-loading VS2008, that and SP1, FW3.5, FW3.5 SP1 etc.

What would cause this?   Why would all old copies of the same solution also fail?



Also, I can't create any NEW projects -
 
I tried creaing one called "TEST" and got the following message.
 
Creating project 'TEST'... project creation failed.
 
 
 
None of the projects will compile, either. All fail!
 
I get the following message for each and every project:
------ Build started: Project: XsltObjects, Configuration: Debug Any CPU ------
Error: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.



I also get the message:  Microsoft Visual Studio has encountered a problem and needs to close every single time I exit the program.  (Sent that "error report" probably 50 times to MS)
I've reinstalled it 3 times now - same issue.
Running on Windows XP Professional SP3 (32bit) and Visual Studio 2008 Standard.

I'm completely stumped on this one, and the only thing recent would be running Microsoft Update (which updated the FW 3.5 and VS2008 to SP1 - but "Downgrading" does nothing, either)
I've opened up permissions on all the folders where the projects/solution resides to all users (GodMode) and services (ie security is wide open).

I'm at wit's end here as not a single solution has worked since Monday.
Anyone?  I'm open to ANY suggestions, tools, hacks, hotfixes, ANYTHING!