An external hard drive would probably be a bit faster, especially if you use Firewire. If you already have a complete backup of your PC, you can use that to save even more time. Another option is taking the drive out of the PC and putting it in an external enclosure that you can connect to your MBP. Yet another option is sharing the itunes folder on the PC over the network. If the PC, Mac, and router, and everything in between all support gigabit, this may be the fastest way. Don't try it over wireless unless you are using wireless N, but even then a wired connection will be much faster.
Which ever way you do it, just replace the (i'm assuming empty) itunes folder on the mac with the one on the PC. Then when you go into itunes, you will need to authorize your music by logging into your itunes account so it will play on the new computer.