Going back to Windows just because of this seems a bit radical. If PyXML is what's required, doing the following seems rather straightforward compared with some DLL conflicts:

1. Download PyXML-0.8.4.tar.gz from http://sourceforge.net/projects/pyxml/files/
2. You may need to install python2.6-dev, for example via: sudo apt-get install python2.6-dev
3. Use these commands:
tar xvzf PyXML-0.8.4.tar.gz
cd PyXML-0.8.4
wget http://launchpadlibrarian.net/31786748/0001-Patch-for-Python-2.6.patch
patch -p1 < 0001-Patch-for-Python-2.6.patch
sudo python2.6 setup.py install

I still reckon PyXML should be packaged in its own package (if the other things in python-xml are broken). I think the patch is easy enough for it to be dealt with as part of the packaging process. Libxml2 may be the modern way to do XPath in Python, but having all the legacy applications (whether-or-not packaged by Debian/Ubuntu) that currently rely on PyXML change their code to use libxml2 sounds like a lot of work, possibly unrealistic.