locate file in package?

[D. R. Evans]

I have just started experimenting with kubuntu, after years of working with
Mandrake/Mandriva.

I have a simple question. Suppose that I want to install a package that
will install a particular file, X. How do I determine which package will
provide the file X?

(In Mdv, this is the "find in file names" search option when installing a
package with the Mandriva Control Center -- that's the functionality I'm
trying to find in kubuntu.)