Will a lens from a Ricoh KR-5 SUPER II w/ a K-mount lens system work with a Pentax ist-DL, 6.1mp, DSLR camera?

I doubt it. The Pentax can accept a KAF2, KAF or KA lenses but the KR-5 seems to be a manual SLR camera instead of motorized one.

Even if the mount fits, you're going to have to manually focus your lens.

A quick check of the Shutterbug magazine review of the Pentax ist-DL and the answer to your question is "YES!"