Since 2.1.102 securelevels were removed and capabilities were introduced.
However capabilities requere modified vfs. In reality this means that
2.2.xx kerneles are less secure then 2.0.xx. Improved securelevels
were added after Solar Designer's  secure Linux patch  was released for 
2.0.33 kernel. In fact, securelevels scheme used in 2.0.3x was never
featured in 2.1.xx or 2.2.xx kernels. There were attempts from some
individuals like  Pavel Machek   to add capabilities in ELF headers.
However securelevels still remain best way to protect your system.
This will probably change somwhere in 2.3.xx or 2.4.0 kernels.

Here is quote from secure-linux.2.0.33.diff:
  "Securelevel limits the capabilities of root, to protect against an
  intruder wiping out the logs and backdooring the system. On an ext2
  filesystem, log files can be marked append-only, and critical system
  binaries marked immutable. This typically needs special support from
  /sbin/init to be able to increase securelevel at bootup, and decrease
  it back when required (for example, by booting into single user mode,
  which ensures physical access to the system). Unfortunately, with
  standard Linux kernel it is too easy to get around securelevel. This
  option adds extra checks to fix the most obvious problems, doesn't
  allow setting the date when securelevel is increased, and also allows
  increasing securelevel via sysctl(). Note that it disallows any direct
  access to the hardware, so you will not be able to start new X servers
  and svgalib applications after you increase securelevel (such existing
  processes, if any, will continue running). Sorry, but this is the only
  way to make securelevel really secure. This doesn't seem to be a
  problem in places where securelevel is really required -- servers, and
  not workstations."

To have securelevel in 2.2.xx you need  patch  and  securelevel.c  that
should be started from /etc/rc.d/rc.local (to compile just do gcc -o 
securelevel securelevel.c> To apply patch do following:
cp securelevel2217.diff.gz /usr/src
cd /usr/src
gzip -cd securelevel2217.diff.gz |patch -p0
cd linux
and rebuild your kernel. Do chattr +i and chattr +a on all files you
consider important (e.g. /etc/rc.d /usr/ /sbin /bin /lib should be
chattr +i -R; /var/log/messages /var/log/kernel should be chattr +a).
I also suggest that you apply Solar Designer's patch that can be found
at: http://www.openwall.com/linux. Until capabilities are fully implemneted
this is the only way to make your sistem really secure. If you need to
change something on running system you will have to do following: boot 
your system from console. At LILO prompt type: linux init=/bin/sh -i 
(presuiming that your image is named linux)or linux init=/sbin/init 1 
After you boot into single user you will be able to perform changes you 
want to your system. Securelevel scheme first appeared in BSD.
NOTE1:
IF YOU WANT TO BE ABLE TO DECREASE SECURELEVEL ON RUNNING SYSTEM:
Change line in kernel/sysctl.c:
if(level < securelevel && current -> pid != 1)
to this:
if(level < securelevel && MAJOR(current->tty->device) != 4)
This way you will be able to decrese securelevel on running system
from system consoles. Of course, change securelevel.c where it
says:
int level = 1; to 
int level = 0;
compile it and name it decrese. If you start it from console you will
be able to decrese secure level. After you finish what you wanted
you will be able to switch to securelevel 1 once again (simply
start original securelevel and everything will be back to normal state).
It was quite frustrating to change to single user every time you have
something to change.


* NOTE! * WARNING! * NOTE! * WARNING! * NOTE! * WARNING! * NOTE! * WARNING! *

SECURELEVEL.C WON'T RAISE SECURELEVEL TO 1 UNLESS YOU PATCH AND RECOMPILE
YOUR KERNEL. IN OTHER WORDS SECURELEVEL.C IS USELESS UNLESS YOUR KERNEL IS
PATCHED AND RECOMPILED!!!!! SECURELEVEL.C IS ALSO USELESS UNLESS YOU MAKE
IMPORTANT SYSTEM FILES AND DIRECTORIES CHATTR +i AND SYSLOG FILES CHATTR +A!
PATCH IS FOR 2.2.17 BUT SHOULD APPLY FOR 2.2.19 ALSO!!!!!
IF YOU DON'T KNOW HOW TO PATCH AND RECOMPILE YOUR KERNEL YOU WON'T NEED THIS
EITHER!!!!!!!!!!!!!!!!1

* NOTE! * WARNING! * NOTE! * WARNING! * NOTE! * WARNING! * NOTE! * WARNING! *

added 26.9.2004:
PATCH FOR 2.6.8.1 Port for linux-2.6.8.1 ext3 attributes included