You can view your notes and highlights on K4PC if you copy both the exact book file and the accompanying .mbp into the My Kindle Content folder where your K4PC books are stored.
Then you'll at least be able to see your marked-up stuff when reading the K4PC copy. At least, this is how it works for my K4Mac install and the older K4PC I've got running under Wine.
But it's a one way trip, as the new format that K2+2.5 firmware and K3 use for .mbp files is different from the one that K4apps generate when you add notes & highlights and the K2/K3 will not read a similarly transferred file that that originated from the K4app.
Amazon really ought to include an "export notes and highlights" feature now that they've broken the old way of extracting them using the MBPReader script
Hope this helps, and welcome to MobileRead!