Here is my presentation I gave at SD West (format - PPT/Zipped). Also available is the sample BPEL and sample WSDL I referenced during the presentation. Feel free to contact me if you have any questions.
BizTalk 2004 supports BPEL. If you haven't yet seen BizTalk 2004 you should really take a look. The product has been totally redesigned from the ground up to take advantage of web services. There are also some additional features such as support for importing/exporting BPEL and Business Rules that you won't find in most other integration servers.
Here are some great resources to learn more about BizTalk 2004:
Online Demo (Flash required).
White papers on SOA, EII and BPM (no registration required)