Epic's Steven Polge posted a quick update on the bonus pack to the official boards:

We are working hard on testing the bonus pack. All the content and code going into the bonus pack is complete, but we are still testing, finding bugs, and tweaking. The bonus pack requires the patch, so we will have to ship the patch first.

"The patch" he refers to is the newest UT2003 patch, currently in beta testing. And in case you forgot, there will be two bonus packs, as Digital Extremes is working on one as well. from this article here: Planetunreal.com