Magento - How can i change magento default ZipCode,Based on my products? (default)

Magento - How can i change magento default ZipCode,Based on my products?
(default)

I've got this problem that I can't solve. Partly because I can't explain
it with the right terms. I'm new to this so sorry for this clumsy
question.
Below you can see an overview of my goal.
In my Shopping site i have a Seller account,In that i am going to add a
product for that i have to give Country,State,City,Zipcode (Store
Details).
If a customer going to buy this product means it should calculate the
distance from My Store ZipCode to Delivery address based on this only have
to generate Shipping cost (only for this product remaining all has to same
as default).
for this i tried a lot but no use even i couldn't find which files i haf
to do modifications also
For this i'm using Magento CE 1.7.0.2 & I'm in learning stage with this
technology
Can any please give some ideas ?
Thank you very much... :)