Generating Letters

Hi, I am looking for tutorials related to generating letters.

If possible I would like these letters to be generated in Microsoft Word
format, as that way they can be directly imported into my companies records
management system.
I have looked at various methods, Crystal Reports seems a little over kill
for what I need, as I am only importing very basic data to the letter (name,
address, title date ect), I had a breif look at word interop, and that
worked well, but I read somewhere that it shouldnt be used with asp.net -
why is this?

So I am just wondering if anyone knows of any good tutorials to help me
generate letters. Ideally, I would like to run it via a webservice, so that
it can be consumed in more than one application, simply passing a ClientID
of the recipient is all I envisage to call the service.

Any suggestions of tutorials / further reading would be great.
Kind Regards ...