Ross, Macs are extremely picky about which ram is installed in them. That being said, I absolutely hate best buy and suggest that everyone stay as far away as possible from them - especially for anything mac.
Buy Mac RAM from either of these places, and you'll see a big difference:
http://www.macsales.com also known as Other World Computing - they specialize in everything mac and have EXCELLENT customer service, technical support and wonderful products at kickass prices.
http://www.transintl.com - they have a wide array of mac and PC upgrades, including a great selection of RAM categorized by each computer model and when it was manufactured (again, macs are picky - so you need to make sure and get the right RAM.) Their RAM is matched to apple's memory and is covered by a LIFETIME WARRANTY!
Best of luck. Just not at Best Buy.