Should one repeat the tasmi' if the Imaam said it?

Some scholars have said that the recitation of Surah Fatiha is compulsory upon each and everyone regardless of whether you are making the salaah behind the Imaam or not.[1] In such a case you can say the basmallah before reciting the Fatiha but please do note that you are not supposed to recite anything while the Imaam is himself reciting something.

Reference:

[1] http://islamqa.info/en/search?key=tasmiyah