Zip files: generate text file in archive on the fly

I need to provide a download of a zip archive containing three files. This is fairly straightforward in PHP so long as one is working with files that already exist. However, I need to customise one of the files (a simple text file) with the user name and other info before zipping. I see no mention of this in the fine manual, and even googling has led me nowhere. Ideas? Am I missing something obvious? Thanks! -- Dotan Cohen http://gibberish.co.il http://what-is-what.com