читайте первоисточники, ObjectMentor:

RUP is a project framework that describes a class of processes that are iterative and
incremental. RUP compliant process deliver functionality in small increments, each
building on the previous, and each being driven by use cases rather than being the
construction of a subsystem. RUP processes estimate tasks and plan schedules by
measuring the speed of iterations relative to their original estimates. Early iterations
of RUP driven projects are strongly focussed upon software architecture; rapid implementation
of features is delayed until a firm architecture has been identified and
tested.
We discussed a minimal implementation of RUP which we called dX . The principles
and practices of dX were identified several years ago by Ward Cunningham, Kent
Beck, Ron Jeffries, and a host of other developers and methodologists. They have
used this process on several projects with significant success. Because of that success,
they have gathered quite a following. They call the process Extreme Programming; or
for short: XP

т.е. XP это RUP для начинающих. Вам выбирать.