Debian Kernel Update with APT – Reboot Required?

Try uninstalling the binutils, libc-dev, and locales packages before you install the 2.6 kernel. Those packages should not be necessary for the upgrade, and can be reinstalled afterwards.

Not really, as far as I can tell. Aptitude seems to be telling you it'll install a new revision of the 2.6.32 kernel you still have installed, but that doesn't mean it'll make it the active version (the one you get by default when booting). You can confirm this by installing the suggested package and then looking at your /boot/grub/menu.lst file.

If you're sure you won't ever go back to 2.6.32 you can remove those packages by the regular means. Something like this:

apt-get remove linux-image-2.6.32.*

Be careful of any unexpected warnings, of course.

Note that you can use apt pinning to handle the backports more comfortably/safely without having to use the -t parameter to apt-get/aptitude.

In your case I'd try something like this (untested):

Package: linux-image
Pin: release a=squeeze-backports
Pin-Priority: 800

Package: *
Pin: release a=stable
Pin-Priority: 700

Package: *
Pin: release a=testing
Pin-Priority: 650

Package: *
Pin: release a=unstable
Pin-Priority: 600