  We present a search for WW and WZ production in final states that contain a
charged lepton (electron or muon) and at least two jets, produced in sqrt(s) =
1.96 TeV ppbar collisions at the Fermilab Tevatron, using data corresponding to
1.2 fb-1 of integrated luminosity collected with the CDF II detector. Diboson
production in this decay channel has yet to be observed at hadron colliders due
to the large single W plus jets background. An artificial neural network has
been developed to increase signal sensitivity, as compared with an event
selection based on conventional cuts. We set a 95% confidence level upper limit
of sigma_{WW}* BR(W->lnu,W->jets)+ sigma_{WZ}*BR(W->lnu,Z->jets) <2.88 pb,
which is consistent with the standard model next to leading order cross section
calculation for this decay channel of 2.09+-0.12 pb.
