Gnomikian, you could simply add the debian experimental repository to your sources list and download the linux bigmem from that repository via synaptic.
This is what I am running now (2.6.35-trunk-686-bigmem) allowing me to utilize total system memory-RAM @ 4048 MiB.
Go to Synaptic>Settings>Repositories>Third-Party Software, and +Add...
experimental main contrib non-free
reload synaptic, select the origin tab and click on experimental/main(ftp.debian.org) and add...,
linux-headers-2.6.35-trunk-686 (Header files for Linux 2.6.35-trunk-686-bigmem
linux-image-2.6.35-trunk-686(Linux 2.6.35 for PCs with 4GB+ RAM