Hey krazykasper,
Could you answer a few questions for me about your files and aims?! I think that it could be possible to help you with some form of VBA code to suit your needs, I just need to have a bit clearer a picture of where I'm starting with this!
- You say the customer name ALWAYS follows a date - so are the ONLY instances of a date the ones that come before a customer name?
- What format is the date in: 02/02/09 - Feb 02 2009 - etc.
- Are you also looking to batch import the letters into one file? before the rest takes place?
Have you not thought of generating a separate Report in your db that would do all the sorting and merging for you? Then you would only need the bit of code to add the Heading styles (which is pretty much the simplest bit to make really! - though thinking about it, you should even be able to get the Report to add the heading style already!!). it's even possible to use a command button on a form in Access that would print the letters as you do now, and then save the new report afterwards - all with one click!
If you are still determined to do all this in Word, then let me know the answers to the questions at the top and I'll have a go at putting something together for you ...