using Air Port express to add N to existing network

I will be purchasing an apple tv tomorrow and will be using it wirelessly on my network. Right now I have a wrt54g as my router. I don't really want to tear my network apart to add put in a new router, pulse my macbook and mini that I use wirelessly are only G anyways. My question is how good is the antenna on the air port express? I was thinking of having it plugged into my router in bridge mode and just using it as an N access point for my apple tv and future N compatible products. This way my G devices don't pull down the speed of my N devices. Do you think this is the way to go or should I just spend the money on an air port extreme base station and piggy back my wrt54g on that?