I have an iMac with an 802.11 a/b/g adapter and I'm planning to purchase to 802.11N Airport Express. 1) Is is imperative for me to enable my current adapter for N? 2) When I try to install the Airport Extreme update I get an error claiming my destination drive cannot install the update. I have 210 GB free. I ran a "permission" program from Apple Support but it didn't fix the problem. Thanks for any thoughts.