How can I do live calculation shipping for UPS and FedEx where the person in the checkout has to select if they are shipping to a home, or shipping to a business. The rates are different, they're cheaper for shipping to business, how can I incorporate this into the shipping calculation in the shopping cart?
If you use UPS as your realtime rates provider, then during the rates call UPS will determine residential vs. commercial and return the correct rate to your CS-Cart store, UPS does a very good job of making this distinction during their AVS.
Fedex does not currently offer this functionality in their API and will return all rates based upon a commercial address assumption, thus unless you have a compelling reason to go with Fedex, then UPS will be your best choice between the two carriers. 
Interesting, thanks for the response. I guess UPS is preferred then. Especially considering the fedex viral video: FedEx Driver Tossing Computer Monitor Over Fence Official Viral Video - YouTube
Your welcome,
And yes, Fedex does have at least a few monkeys on their payroll ! 