Thanks for the reply.
Just done as you suggested and the xmltex error has come up again.
I have tried 'downgrading from the testing to the stable but it keeps throwing up:
The following packages have unmet dependencies:
xmltex: Depends: tetex-bin (>= 1.0.7+20011202-5.1) but it is not going to be installed
Depends: tetex-extra but it is not going to be installed
E: Broken packages
I'll work this out eventually. Again, thanks for the reply.
UPDATE: I think I have. I set tetex-bin, tetex-base and tetex-extra to the testing releases (rather than a lot of stuff coming from unstable). These have enabled me to remove xmltex for the time being as it caused all sorts of problems. All seems well again for the time being.