Extending a Wireless Network

Ok; so I've read through a few posts on Airport Express, but didn't find my specific topology so I wanted to see if anyone could tell me if they've run this way before.

I have an Airport Xtreme Base Station right now. I'm on a wireless internet provider whose service sucks balls. Anyway I'm pretty set on pulling the trigger on a switch to Cable but there's a problem. I have satellite TV and as a result my only viable cable jack is upstairs while all my equipment including my Canon USB printer and NAS are downstairs.

What I was considering doing when I switch was buying an Airport Express, running ethernet from the cable modem to the Express and setting up the Express as a wireless access point. I would then use my Airport Extreme downstairs by extending the wireless network created by the Airport Express thus leaving everything connected to the Xtreme downstairs as it now.

I've seen info that you can definitely have the Express extend off a wireless network on the Extreme but I haven't found confirmation that you can have the Extreme extend off the Express. Has anyone been able to successfully configure their network in this way? Is this possible?

Thanks!