CORBA vs XML: What is important to understand is that CORBA is not just a declarative language. It truly is the middleware architecture/framework. You don't have to worry about how this request gets to the client from the server or from the server to the client ORB does it for you. XML on the other hand is just a declarative language.
We use Visibroker as our ORB. When it comes to deployment you need to have an ORB implementation on the client side (Netscape comes with Visibroker 3 classes, maybe Netscape 6 comes with Visibroker 4 but I am not sure).
CORBA is VERY powerful and so far Visibroker has stayed ahead of its competition on full compliance with OMG specs and additional *very useful features* features.
As far as B2B exchange IMHO XML is a better fit for it due it's flexibility ans easiness to change message structures going back and forth. You can send XML over CORBA if you need to. However beware of parsing overhead. When it comes to speed and necessity to provide some good numbers performace wise then CORBA is your answer. The only thing that is faster than CORBA that I know of is socket-to-socket :-)