The kernel you want is the latest in the 2.4.x series. The versioning system in Linux, and in many apps for Linux, may appear strange at first, but you quickly get used to it, and it does make a lot of sense.
Currently the kernel version is 2.4.21. The 'development' (read: unstable) version is 2.5.69. The odd number in the middle (2.5.69) denotes development status. The numbering system for the last digits is linear, so .1 is early and .10 is later - they are not the same thing.
Hope this helps. Still confused? Post again!