Kernel sources for Debian kernel 2.6.18-6-686

[Oliver <osoeder@gmx.de>]

I just installed Debian with a netinstall CD.

uname -r tells me that I am using the kernel 2.6.18-6-686.
Now I am installing a driver (Diva for Linux) and this driver needs
the kernel sources to compile a .deb package.

(Instructions on page 17 of this document:
http://www.dialogic.com/download/p/linux/source.8.5/108-80/Diva_SR_LIN_ReferenceGuide.pdf)

I really do not know where to find the sources for this kernel
version, as it is a customized Debian kernel.
If you can not help, I need to download the newest kernel from
Kernel.org and recompile?

Thank you for you help

Oliver