Random code gen and send with email

i want to be able to generate a random code (and put text in the line above it), put it in a text file, and send it with sendmail. I have the sendmail command working, but i need the code (15 characters) in a specific place (fifth line) because of sendmail. How can i do this? Oh, and i also need it to create the from and subject lines in the text file. And im bad at complicated applescripts, and i was too lazy to figure it out myself (text has given me LOTS of problems in the past).