Auto update shipping methods when zip code entered

Hello, I want to auto update the shipping options (methods) at the checkout page when a customer enter the zip code for billing or shipping address.
I need to do it because I use Table Rates methods and the shipping costs calculated from the zip code.
And we use Checkout Manager we hide some of the checkout fields, such as the Country, Company Name, and some more fields, to short out the checkout page.
If I can do it with AJAX it’s prefered… Thanks a lot!