SOAP in thunderbird 3.0a1pre

Hi, I'm working on porting an extension to thunderbird 3.0a1pre and am 
working with the current version from:
http://ftp.mozilla.org/pub/mozilla.org/thunderbird/nightly/latest-trunk/

What I've found is that the current release doesn't seem to know about 
SOAP.  When this is copy/pasted into the error console:
   typeof SOAPCall;
... in thunderbird 1.5 and 2, it reports "function", in 3.0a1pre it 
reports "undefined".

Can anyone shed any light on why this might be the case?  Also, is there 
anything I can do to get SOAP under 3.0?  eg. building from source 
rather than using the win32-installer.

Thanks -

Leni.