there is a mailmerge package available. I think that it's somewhere as a contrib package on the site, but I'd have to look. If that fails & you need it (or want to code more of it :), I can send the most recent version. It's not done, and a couple of the options don't work yet (seems to me that separating by a paragraph marker is one of them), but it worked well enough to send out 200 job applications :)
And it's done in the text-based way of the 80's word processors, rather than the brain-dead way word & staroffice do it. --