Hm, the problem doesn't seem to be related to the 'powercommands' extension after all. In fact, the powercommands extension wasn't even the one that caused my 'Add Reference' window to look different (I must have had another extension installed, I can't remember). I am seeing the same problem now: in a new VB winforms project, System.Design.dll is not in the list. Strange! I've seen this before, and I've been able to solve this before, but I cannot remember how I'm sure I'm going to need it soon enough though so I'll probably get back to this then lol...

Can't you switch to .NET 3.5, add the reference, and then switch back to 4.0?