Lot of my friends seems to get confused on Contact Hours and PDUs. The main difference between Contact Hours and PDUs is that Contact Hours are accumulated prior and PDUs after your PMP Exam. You need 35 Contact Hours before the exam and after you become a certified PMP, you will need to accumulate 60 Professional Development Units (PDUs) every 3 years to keep your certification current. However the content of the training can be identical.
The contact hours can be accumulated by attending project management related training.