the following three sets of numbers comprise the Linux kernel versions:

Major umber: this number indicates the version of the kernel. this number is incremented only when there is a significant change. such as when support for the major new hardware configuration is added.

Minor number: the minor number indicates a minor revision and its reliability.

Revision Number: the revision number identifies the exact version of the kernel you are using and is incremented on every release.

for example: 2.4.21

the major is 2
the minor is 2
the revision is 21

simple right?

not sure what version to get? well, because the Linux development community is always writing new kernels and releasing them for testing, there are many different version available at once. you could make a big mistake by upgrading your kernel every time a new one comes out. many of the versions are experimental, not tested and may be unstable on your computer

the biggest clue to a kernel's reliabilty is the minor number.

and ODD minor number means a development kernel, a version that is not fully tested and might be unstable and have bugs.

an EVEN minor number means which is also called a production kernel, this is a version that has thoroughly tested and considered reliable enough for a mission critical system or like a production server

for example, lets say if the kernel number 2.5.74, there might be a problem with this version. then your probaly want to wait until a 2.6 version is released before trying to the newest version