Well, I found my list at:

HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\ComDlg32\OpenSaveMRU\pst

The value, MRUList, data lists the values of all pst's currently(?) loaded. So, read MRUList, and then each character is a value in the same section which points to the pst.

Thanks Glenn! Learn something new everyday. \:\)