Airport Express Bridge Question

[RMSko]

I have an Airport Express that has a wired Ethernet connection to a single band (2.4Ghz) Linksys router (E1200). I set up the AE to "create a wireless network" and also as a bridge. I basically want it to be its own network that isn't "dragged down" by some of my G devices (I have them connecting directly to the Linksys) and so I want to have setup the AE solely to operate under the N network. I'd also like to have it operate under 5Ghz instead of 2.4 Ghz and I would think b/c it's a wired connection to the router that the router being 2.4Ghz shouldn't matter. However, I haven't been able to get my new MacBook Air to connect to the 5Ghz connection and I'm wondering what could be the problem. I posted this on the MBA forum, but realized it's really an AE question and I thought it makes more sense to post here. Any thoughts would be really appreciated?