Deserted,
As your question is related to a job that you're being paid for, I don't think you'll get much of a response here without signing up for a Premium Support membership (
http://www.d-a-l.com/help/subscriptions.php) - it costs next to nothing really but it means that we'll know the site is getting some much-needed income in return for us helping you out in our spare time (which we all do for free).
Incidentally, if I had this problem and wanted to think of a quick answer before I headed off to bed (which is exactly what I'm about to do!), I'd go to
www.microsoft.com/downloads and look for an updated version of Windows Installer. It's available on Microsoft.com as a redistributable file so you don't need to use the client's PC to run Windows Update or anything - use whatever system you've got hooked up to the Internet and some form of then getting the download onto the client's PC, e.g. USB drive, CD, etc.