Okay I've completed my mail merge version done in Word and Access 2000 (both files in the attached zip).
Put your data into the database using the form, there is some sample data there already feel free to delete it (but not the table structure). Don't put the skill values in for Listen and Spot twice as the mail merge does it anyway.
The database has a sample data field in it just so everything had some data, which made it handy for editing the mail merge document. The second line of data is just a example monster. There is a form to allow for easier data entry. I had originally panned on doing it with just and excel spread sheet but there were just so many data fields that I switched to access.
It's not been tested thoroughly so let me know if you use it and have problems.
Known issues...
The magical abilities field in the database is so you can add stuff like Spell Known/per day/memorised Spell-like Abilities, Power Points, etc. etc. You'll have to format them youself after doing a mail merge. I was just to lazy to put separate field in for all of those.