Time machine question

I recently helped my Uncle and Aunt purchase a refurb macbook pro to replace a dead iMac G5. They have been making CD's of their pictures as back ups. Not the most efficient backup solution, but it is a back up at least. I have convinced them of the benefits of an external hard drive for a time machine back up. They are using an airport express for their wifi (model that plugs directly into the wall socket). Now my question is can I directly plug in the hard drive to their macbook pro for the first initial backup and then plug that drive into the airport express for over the air time machine backups?

via ehMac.ca http://ift.tt/1sCJmpq