USB to RS232

I want to convert the USB signal into RS 232 or BT..
Actually the output of the IRIS sensor gives the USB signal..Then by using a tiny microprocessor,
i have to convert the USB into UART.. (i.e.,) or simply we can say USB to UART converter..

So,i need to program for that microprocessor.. So i want to know that as follows

1.Is it a big task without the development kit????
2*.If not How to develop it?????
3. At last What should i look for choosing the suitable microprocessor in this project??