Slack uses (used to use) the stock
kernels from kernel.org, thus there
has never been a need to roll releases
of each new patch...
In Slack 9 the kernel has been patched
to support jfs and xfs, I think... :) If you
didn't use either of those for your install
just continue using kernels from
http://www.kernel.org (or a close mirror)
Cheers,
Tink
P.S.: The current latest stable from
the 2.4.x branch is 21, more up to date
is patch-2.4.22-pre9