What you need to use is a feature of apt-get called holding
You can either do this via Synaptic or Dpkg, Here is how I would hold my kernel using the dpkg method.
First check your kernel image name
dpkg -l | grep linux-image
output for me:
ii linux-image-3.2.0-4-amd64 3.2.35-2 amd64 Linux 3.2 for 64-bit PCs
ii linux-image-amd64 3.2+46 amd64 Linux for 64-bit PCs (meta-package)
then tell dpkg to hold the metapackage (the generic version without any version numbers)
echo linux-image-amd64 hold | sudo dpkg --set-selections
You can then check this worked via dpkg -l linux-image-amd64
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-==========================-==================-==================-==========================================================
hi linux-image-amd64 3.2+46 amd64 Linux for 64-bit PCs (meta-package)
Notice the 'hi' at the bottom, h means held and i means currently installed. This package is installed but will not be upgraded.
You can reverse this via
echo linux-image-amd64 install | sudo dpkg --set-selections
and again can check via dpkg -l linux-image-amd64
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-==========================-==================-==================-==========================================================
ii linux-image-amd64 3.2+46 amd64 Linux for 64-bit PCs (meta-package)
Notice 'ii', the first i means this package is set to install and the second i means it is currently installed. This package is installed and will be upgraded.
For more information on these flags see man dpkg
specifically the 'package selection states' sections.