I'm sure there are dozens of mail-merge programs available for Windows that you can use. You supply the body of the email and a list of email addresses and names - it takes care of the rest.

For the Mac, I use a program called Direct Mail which has worked quite well. I've probably only sent out 1 mass email per year in the past three years, but each time the program was a massive time saver. It also allows spacing out the sending so you don't run into trouble with hourly quotas on you mail server.