Proof of Gauss's lemma for Polynomials

[Swistaq]

Do you know an easy proof of Gauss's lemma for Polynomials?
If a polynomial with integer coefficients is irreducible over the integers, then it is also irreducible if it is considered as a polynomial over the rationals.
It's sounds little unbeliveable....

[t0rajir0u]

The proof in the Wikipedia article is straightforward.

[Swistaq]

Reading the Wikipedia article was the first thing I'v done. The first part (the proof of primitive property) is ok. But the strict proof of lemma is worse. I hope it can be told using less complicated words ...