missing package (maybe just clueless user)

[g b <descartavel.1@gmail.com>]

followed the instructions, installed linux-image-2.6.39-686-pae just fine!

but i can't find linux-headers-2.6.39.*

i'm trying to get this one
http://packages.debian.org/squeeze-backports/linux-headers-2.6.39-bpo.2-686-pae


# aptitude -t squeeze-backports install linux-headers-2.6.39-bpo.2-686-pae
Couldn't find any package whose name or description matched
"linux-headers-2.6.39-bpo.2-686-pae"
Couldn't find any package whose name or description matched
"linux-headers-2.6.39-bpo.2-686-pae"
No packages will be installed, upgraded, or removed.

$ cat /etc/apt/sources.list
deb http://ftp.us.debian.org/debian/ squeeze main non-free
deb-src http://ftp.us.debian.org/debian/ squeeze main
#
deb http://security.debian.org/ squeeze/updates main
deb-src http://security.debian.org/ squeeze/updates main
# squeeze-updates, previously known as 'volatile'
deb http://ftp.us.debian.org/debian/ squeeze-updates main
deb-src http://ftp.us.debian.org/debian/ squeeze-updates main
# BACKPORTS
deb http://backports.debian.org/debian-backports squeeze-backports
main non-free
# do I even need that?
deb-src http://backports.debian.org/debian-backports squeeze-backports
main non-free



What am I doing wrong?

thank you,