The Sun PDF import Extension
is ready for beta testing now. it works with OOo 3.0 which is also in Beta. So don't use these for valuable work, they are for evaluation and test purposes only.
From the Sun description of the extension:
The PDF Import Extension allows modifying existing PDF files for which the original source files do not exist anymore. PDF documents are imported in Draw and Impress to preserve the layout and to allow basic editing. It is the perfect solution for changing dates, numbers or small portions of text. Native PDF forms are not yet imported.
Note: Sun suggest that this is suited to making small changes - they're not trying to replicate anythng near the functionality Adobe Acrobat, and for now it works in Draw and Impress only, not Writer.