1. Regular Cat5 wire can NOT be ran threw metal conduit due to capacitance to the wires. They do make plenum rated Cat5, but you would be better off running plastic conduit.
2. UL states you can NOT run low voltage wires with high voltage wires without classifying all the wires as high voltage. This would prevent you from using standard cat-5 connectors.
So you are better off running separate plastic conduit and combining Phone, CatV and the cat-5 and then use either plastic boxes or "wrap" plates.
note: I am not shure what to call that metal plate that wraps around the Sheetrock so you can add a cover.
Edit: #2 above also means that you have to run two conduits even if you use a divider in the box.