[ edit - i made a lot of references to you having 2.4.24 when you actually have 2.4.22, just ignore me :P ]
Ah ok.
Well im not familiar with the open wall patch ( or any patches for that matter ) but to get to the 2.4.26 I would upgrade all slack packages related to the kernel. kernel-2.4.26*.tgz's. Get it from Slackware-Current. Then get the bare.i folder from the kernel directory of slackware-current.
unzip the System.map.gz as System.map
Now you should have 3 files;
bzImage
config
System.map
you can just remove or rename the old 'System.map' and remove the link 'config' from /boot
now copy your three files to /boot
on my particular box for now reason really i rename 'System.map' to 'System.map.upg' and then created a link
ln -s System.map.upg System.map
and renamed config to config26 and made another link
ln -s config26 config
The above isn't necessary though i just like them to be links just in case i do something stupid inside of the boot folder ( haven't done anything like that yet but who knows )
Now that thats done double check your work, inside of /boot you should have either these files themselves or links to the files, check the links by hovering your mouse over the files or if your in a command prompt just vi the link ( vi config )and if it comes up with junk exit vi.
sidenote: if your not familiar with vi and need to exit hold down shift and hit colon, let go of shift, type a 'q' without quotes and hit enter.
next open /etc/lilo.conf
you will see the following
# Linux bootable partition config begins
image = /boot/vmlinuz
root = /dev/hde1
label = Gate
read-only # Non-UMSDOS filesystems should be mounted read-only for checking
# Linux bootable partition config ends
simply change the line
image = /boot/vmlinuz
to say
image = /boot/bzImage
Save and exit
type
lilo
at the command prompt and if you want to install into the mbr if its necessary on your setup then after typing lilo, type
lilo -M /dev/hde -mbr
Of course change the device as appropriate for your setup.
If its a stock install of slack 9.1 then everything will work fine when you reboot. If you want to be on the safe side then you could just rename the current system.map and config of the 2.4.24 kernel with a .old extension and add the appropriate stuff into lilo.conf
Of course that doesn't get you the open wall patch i imagine eh?
NOW ONTO WHAT YOUR ACTUALLY ASKING
What I would do if i were you is see if they are using a stock kernel from the 9.1 cd. I would get an md5 checksum from the vmlinuz, config, and System.map from the /boot and compare it to the md5 checksum of the same files from a stock install of 9.1
If they match up, et voila install the kernel source from 9.1 then id probably install the kernel source files from kernel.org and get the open wall patch and apply it to the source; then simply copy the config file over from the 2.4.24 kernel source into the kernel source with open wall patch folder that you downloaded, and so on and so on. If you cant manage it from here confidently i probably wouldn't be messing with the server
Alternatively you could download the kernel-source from slackware-current ( which is 2.4.26 ) then download just the open wall patch from kernel.org and recompile. The config will already be there.
If your not familiar with compiling a kernel i wouldn't mess with your server, go read up on it.
Anyways I suggest doing a checksum and if they match up, roll with it