R help - Sep 2007 - variables selection in Aalen and Cox model

Dear members of R community,

   I  want  to know about the R procedures (or routines) to carry out the
   selection of covariates in an Aalen or
   cox model, respectively.

   Thanks a lot
   Luis Guillermo D??az Monroy
   Profesor Asociado Departamento de Estad??stica
   Universidad Nacional de Colombia