Anything is possible.  Which Ricoh lens, is it a K-mount, a
screw mount or other?  If you find an adapter it will need
an optical element (sort of a low-power tele-converter) to
reach the correct back focus for the Nikon, you will need to
use a hand held meter or base exposure on the histogram
since the D50 does not support stop down metering and just
flat out be inconvenient.  Expect to pay around $100 for
such an adapter.

Unless the lens is "very special" (and I don't know of any
"very special" lenses in Ricoh mounts) it's probably not
worth the bother, on the other hand IF you had a whole kit
of Ricoh lenses in a Pentax type mount you'd be better off
with a Pentax dSLR, like the K100D.
darkroommike