"Fork failed" means that it cannot spawn a new process/thread.
This may be down to your version of Windows - I know 2003 has a whole lot more 'security' settings that can prevent things from running as expected.
I also know that Open Innovations (who make the bundle - email them directly on their web site) are planning on making a new bundle as the old one is very out of date. Hopefully the new bundle will be tested on 2003!
I've not heard of this particular install problem before though, anyone else installed the Bundle on 2003?
Your other option is to do it by hand. The ISO image of the Companion CD (free from http://www.steveshipway.org/book/
) has the windows versions of RRDtool, Perl, and Apache for installing plus MRTG and Routers2. It would be a bit more work, though