Extend wireless network with a Mac Pro?

Hi

I have a couple of airport expresses that are extending the range of the wifi network thats provided by an airport extreme - everything works fine. I have a macpro in the garage thats a server for the network and is wired on the network. I can use this mac to use create a 'new' wireless network using its airport card but what i'd really like is to 'extend' the current network so that devices dont need to switch networks and just roam to a new access point.

Back story to this is that i'm trying to get better wifi coverage in the garden and the garage is in a perfect spot for this, and it works fine, but only on a different SSID. Any thoughts if this is possible or would i need to buy yet another airport express? I had thought of just using the same SSID with the same password but this could cause other issues i am sure.

any thoughts?

Hi

Thanks but thats not the case as i have cat 6 into the garage - I could easily put another airport express in there and use this but what i actually want to do is use the macpro to BRIDGE the network to the airport card in there so i am not double nat'ing which i am at the moment as i'm using the airport card to share the network connection provided by ethernet.

I might get creating with ipconfig and try to manually configure a bridge but i would have though i am not the first trying to do this with the hardware i have available.

cheers