Enhance Wifi range on a TimeCapsule
Run iStumbler from your Mac.  (Get it here). Look at the other wireless networks in your vicinity - and check what channel(s) they're running on.  You want your device to be as far away from those channels as possible.  There is a 3-channel overlap.  That means, a device on channel 1 will interfere (albeit only slightly,) with a device on channel 3 (or 4?  I forget.)  So if lots of devices are on channel 6 (most come out of the box on this channel,) you want to be on 9/10/11 or 3/2/1.  I almost always just use 1 or 11.

There is also a "use network robustness" option which I think increases range but decreases bandwidth.  See this Apple Article.