locating cities within a radius of another

We need to locate all cities within a certain distance of a single city.
  We have longitude and latitude data for all cities.  I was thinking
postGIS was a viable solution, but I don't see a way to use our existing
data via postGIS.

Is postGIS a viable solution, or should I be looking at a different
approach?  Thanks for any suggestions or RTFM pointers.

--
Until later, Geoffrey

"I predict future happiness for America if they can prevent
the government from wasting the labors of the people under
the pretense of taking care of them."
- Thomas Jefferson