Actually it will really depends on the results of the first row.
If Sarkozy doesn't pass the first row, it will be either:
*Hollande-Le Pen (very likely)
or
*Le Pen-Bayrou (very unlikely)
=>in either cases Le Pen would lose because all center and left voters will vote for the non extremist candidate.
In the case of a Hollande-Sarkozy or Bayrou-Sarkozy second row, it is hard predict something because the two candidates would be too close politically (on the european issue for instance). But we can guess that Sarkozy would search to appeal to Le Pen voters (which he is already doing) and would eventually win by a thin margin.