Today I passed the 70-642 Network Infrastructure, Configuring exam! I found this exam a bit easier due to being more focused in the objective scope than the 70-640. The DNS studying for the 70-640 should mostly over lap with the 642 which should give you a head start to your studies. My strongest section was configuring name resolution and my weakest was configuring network access. Overall I was happy with my performance on the exam and more importantly the skills I picked up during studying.
My next goal is to try to finish the 70-646 before the end of December which will complete my MCSA Server 2008 and MCITP: Server Administrator certification.