Hot diggety dog! IBM and Novell are teaming up to add XForms support to Mozilla! If I were Microsoft, I'd be very, very worried right now.
More immediately, IBM has updated their XML Security Suite with "XPath Filter 2.0 support and lots of bug fixes." This is a Java class library that supports XML encryption, digital signatures, and canonicalization. It's officially supported on Windows and Linux but will probably run on other platforms. It's mostly a programmer tool. The user interface ranges from porr to non-existent.