Infrastructure Software

I am facing problems with installing the Cisco VPN client for linux (vpnclient-4.8-orcl-hybrid.tar.gz) on my Fedora Core 6 system. The problem I face during install is a missing linux/config.h file. This is what I have tried already (from various forums/posts etc etc) -

1. FC6 by default installs a i586 kernel. I have changed that to i686 to reflect the arch.
2. Kernel source is installed and I am providing the correct source paths for the kernel (from /usr/src/kernels and linked elsewhere)
3. Linking config.h to different headers. It complains about each one of those scenarios (people have made it to work somehow in other systems) and I am tired of those hacks.

Is this a known bug? Are there any other versions of the client that work? Newer or older?
I would appreciate any helpful response in this regard.