I moved my Mac Mini a little further away from my AEBS and found, through the wireless clients list, that it was now connecting to the 2.4 GHz network. I wanted to find a way to force the computer to always connect to the 5 GHz band, since that's what my MacBook Pro was able to do from the same distance. All the info on the Net said the only way to do it was to set up two different network names, but that would have killed my easy transition to the kitchen, which can only pick up 2.4 GHz, forcing me to manually switch networks often.
The new version of iStumbler for Snow Leopard saved the day.
iStumbler 99 showed that the Mini was seeing the 5 GHz network at 41% signal strength and the 2.4 GHz at 42%. That was apparently enough for the AEBS to automatically connect the Mini to the lower band. I opened up iStumbler on the Mac Mini and double clicked on the 5 GHz version of my network -- the one with the 166 channel number. iStumbler forced the Mini to connect to that particular network.
Now I'm connected the the 5 GHz whether the AEBS likes it or not, which is confirmed in the AEBS wireless client list as well as the extended network info when I option-click the menubar icon.
[crarko adds: I haven't tested this one, but iStumbler is another of those handy utilities to add to your toolbox.]

