Compiling old kernels

[HUNTER]

I'm having a kernel related bug and it appears that I'm the only one who
has it so it looks I have to find it myself.

I'm going to compile several different version of kernel in order to
figure out the exact revision when and where the bug was introduced.

I have several questions:
1. How to update the source code to a specified version with revision
numbers and tags? I have some experience with SVN but git is different
and I'm not familial with it. Besides I don't know Ubuntu conventions
regarding the repository.
2. I'm going to start from the latest kernel which is known to work
well: 2.6.26-1-rt. The problem is I don't know which version of source
code it was based on.
3. I'll have to install DEBs, ignoring dependencies. How to make it
ignore dependences? Is it dangerous for the system? In particular, does
it affect ofter kernels or configs(apart from the menu.lst)?