Upgrade from 2.4.25 to 2.6.4 kernel

[Job 317]

Hello list.

Can someone please point me to a HOWTO on installing a 2.6.x kernel on a
system that heretofore runs a 2.4.x kernel? 

NOT a howto on building the kernel. I'm o.k. there. But I understand
that it is not the same upgrading to a 2.6.x kernel as it is just
upgrading to the next 2.4.x kernel. Is this correct? Aren't there
startup scripts and things that rely on the 2.4.x structure that change
slightly for a 2.6.x kernel?

!!!!Also... is it possible to still to boot back to a 2.4.x kernel in
this case? Lets say I keep my 2.4.25 kernel that I built on my RedHat 9
box. Can I also boot to and from my 2.6.x kernel?

Thanks.

JOB