If you've outstayed your travel visa time limit, going into mexico and then coming back into the U.S. is risky. My girlfriend (Italian) and i tried this. It work with the grace of God but only after one of the most dramatic exeriences of my life, not to mention a night in jail for her. But hey she stayed in the U.S. another three months. Normally, the border patrol told her, you get deported, but in her case they made an exception. Good luck if anyone wants to try this.