COMMAND LINE METHOD:
Locking the version on a package prevents it from being upgraded. I'll show you two ways to do this. The first is to open a terminal and type: sudo aptitude hold linux-image-`uname -r` Those ` are backticks, usually located to the left of the 1/! key.
SYNAPTIC PACKAGE MANAGER METHOD:
For those who prefer to use GUIs, open Synaptic and scroll down to where the packages named linux-image- and then some numbers are. Find the one you are using (probably the highest number), and click Package > Lock Version. Both of these will prevent the kernel from upgrading at all.
OK, now you need to release those holds.
Synaptic, that's no problem. Just un-check it, do the upgrade, then make sure you lock version on the new one. For the command line one do sudo aptitude unhold linux-image-`uname -r`. Redo all your tweaks of course, and you're good to go.