Calendar Form to direct to different booking systems

We are in the process of transitioning from one online booking system to a new online booking system.

All bookings after the 1st January 2014 will be required to be made through the new booking systems (freetobook).

To assist the transition we need to customise the booking search form at the top of www.newinglodge.co.uk. For all bookings before 01/01/2014 we require the form data (the date of check in and number of nights) to be posted to the old booking system. For all dates after, posted to the new system.

I can send the code for the 2 different forms. What is required is integrating these into the website with the above logic so it seamlessly sends you to the correct booking system when the customer searches for availability.