I have implemented the mentioned code in all of the previous code and I tested it and it works great as far as I can see.
What I tested:
* Product with defined shipping freight.
* Flat tax rate (added extra code to set the default state to another state so tax rate isn't calculated as opposed to changing the default state in the X-Cart admin)
* Combination of above.
I have yet to test it with defined shipping methods but I have added the appropriate mentioned code to handle it. I was wondering what other cosiderations should I be aware of.
Thanks to all the contributors of this great mod.
EDIT:
This seems like a good free PHP solution for ZIP to state conversion. I've seen another that used arrays rather than a bunch of cases.
EDIT: Before I implement FEDEX into the system, I heard that it does not play nicely with this great mod, is this true?