It looks like Fiddler2 might be just what you want. It’s a proxy that captures and analyzes HTTP traffic. Unfortunately, I think you might have to install something on the SOAP server in order to make it work. I didn’t read the docs too deeply, so you might want to check that.
Also, just a reminder that Wireshark must be on the same link as machines that it’s capturing from. That is, Wireshark is installed on 10.0.0.1, and you are trying to capture packets between 10.0.0.2 and 10.0.0.3, then you can’t have a switch between 10.0.0.1 and the other two- Wireshark (or any packet capture) will only get traffic on the link between the switch port and 10.0.0.1’s interface. If you have physical access to one or both of 10.0.0.2 or 10.0.0.3, then a stategically-placed hub will mitigate this.
Does the IT department understand what you are trying to accomplish? They must surely have their own packet-capture setup (necessary for some kinds of troubleshooting) and might be able to provide you with the logs you need. If you can write a filtering rule to pull out the SOAP envelope data then they should be able to implement it for you. If not then they should be fired and your company should hire me instead. IT is there to enable the use of technology, not prevent it!