Exchange is it okay with a broadband modem

Hi All,

I am soon to be setting up an exghange server at our office, we are using a broadband dialup with a static IP one side and a private Ip the other, does the server have to have a static public IP for exchange or can i use port forwarding???
One a seperate note where does the MX record need to be pointing to my server or my ISP..thanks in advance