Bzip2 ?
 

I have downloaded a kernel patch

(i'm so feeling n00b today)

the file is a bzip2 type

How i can install that patch?

filename: patch-2.4.21.bz2

Well first you have to bunzip2 it:
bunzip2 filename.bz2
Then apply the patch:
patch -Np1 patchname

Normally you are in the directory of the files/app to be patched, so if this is a kernel:
cd /usr/src/linux
patch -Np1 /path/to/patch/file/patch

:)

HTH

Cool