If you want to know more about acceptance testing, the Microsoft Patterns & Practices Team has just released Beta 1 of their Acceptance Test Engineering Guide which is available in PDF on CodePlex.
Per the guide:
"This guide is about accepting software. Accepting software involves acceptance testing, but it is much more than that. This guide uses the following terms very specifically:
Acceptance refers to the act of assessing whether a piece of software or a system meets the customers' expectations. It includes both the acceptance decision and any acceptance testing activities required to collect the data on which the acceptance decision is based. The pre-decision testing activities can be considered "readiness" testing; this concept is described more later in this guide. Both the acceptance testing and the acceptance decision can be relegated to a separate acceptance phase of the project or they can be done throughout the project, which is known as Incremental Acceptance Testing."
If this sounds interesting, you can download the Acceptance Test Engineering Guide here.
Whata is Acceptance Testing? Information