UPS integration is provided as a plugin for Zen Cart.
There are two options:
The UPS Shipping module provides retail rates for your cart based on shipping from the zip code entered at: Admin > Configuration > Shipping/Packaging > Postal Code.
The UPS XML module provides the option of receiving retail rates or negotiated rates. To use this module, you must have an XML rate access key. The process for getting an access key is described in the module documentation.