Outlook signature scripting problems in a mixed environment

[JJSRich]

I am using the tutorial from

http://technet.microsoft.com/en-gb/magazine/2006.10.heyscriptingguy.aspx

I know it's from 2006, but it seems to hold the relevant information, and works for my people on Office 2007 and 2010, XP, Vista, and 7. However, it does not work for people on Office 2003. I am at a loss as to why this is the case. Why isn't this scripting thing working for some of my users?