USA, Canada / Working in Italy (Europe in General) US Citizen, Polish born... [2]

Hi everyone...

I was born in Poland some 30 years ago. I had a Polish Consular passport that expired and have since become a US citizen. I now have a US passport.

I remember that during the ceremony to become a US citizen, we had to "renounce" our former citizenship.

Here's the question... I will likely be working in Italy in the next two years. As a citizen of the EU it's much easier to get a work visa. If I leave the US and enter Italy on my Polish passport (which I'd have to get a new one) will I be able to re-enter the US later? Let's say that a year from that time I want to come home to the US, what will US Customs say when I have no stamps on the US passport?

What is the best way to do this? I hear it can take up to three years to get a work visa for US citizens, and that would suck.

Thanks all!