  The experimental errors in current and future hadron colliders are expected
to decrease to a level that will challenge the uncertainties in the theoretical
calculations. One important component in the prediction uncertainties comes
from the Parton Density Functions of the (anti)proton. In this work we develop
an interface from the Les Houches Accord Parton Density Functions (LHAPDF)
package to the very popular Monte Carlo generator {\tt PYTHIA} version 6.2.
Then we proceed to estimate the PDF uncertainties for the production of
Drell-Yan pairs from the Z pole to masses above 1 $\TeV$ and for Higgs bosons
at LHC. The measurement of the electro-weak mixing angle at LHC as a
particularly difficult case is studied.
