Backports.org has released a backport of Kernel 2.6.4 for Debian GNU/Linux 3.0

Packages: kernel-image-2.6-686-smp, kernel-image-2.6-k7-smp, kernel-image-2.6.4-1-686, kernel-image-2.6.4-1-k7-smp, kernel-image-2.6.4-1-386, kernel-image-2.6.4-1-k7, kernel-headers-2.6.4-1-686-smp, kernel-headers-2.6.4-1-686, kernel-headers-2.6.4-1-k7-smp, kernel-image-2.6-686, kernel-image-2.6-386, kernel-headers-2.6.4-1, kernel-image-2.6.4-1-686-smp, kernel-headers-2.6.4-1-386, kernel-headers-2.6.4-1-k7, kernel-image-2.6-k7
Version: 2.6.4-0.backports.org.1
Achitecture: i386

Here the apt sources:

# Kernel 2.6.4
deb http://www.backports.org/debian/ woody kernel-image-2.6.4-i386

A nVidia Kernel for 2.6.4 is available here:

# nVidia Kernel 2.6.4
deb http://www.backports.org/debian/ woody nvidia-modules-2.6-i386