Miles transfer between programs
Rachel - Your UA miles will not transfer, but since both airlines are both code share partners and Star Alliance partners you can use your UA miles for US flights in many cases.
US should be willing to match your Premier Executive status to either Gold or Platinum status depending on how closely they look at your UA travel history. The new Platinum status normally starts at 90 segments through 119 segments or 75,000 to 99,999 EQM's so the UA Premier Exec category over laps US Gold and Platinum.