There is already the 2.6 Kernel out. You are sure you want only kernel 2.4.28?
My personal recommendation for you is to get the 10.1 Mandrake cds. Backup before installation all the programs you want to keep and are not with mandrake. Then make an fresh installation and when he asks for the partition take over the old one and format only /usr / but NOT /home where all your personal data are. Though you can keep all your personel staff and get quitefast all upgrades on Kernel kde and all the other goodies.
If you are really willing to compile your kernel fresh, got to the www.kernel.org
and fetch the kernel source you want. Than go the mandrake manual with the Howtos. There is an execllent desribtion for how to do it. Following that I was able to create my own kernels. Takes time.