kernel compile
 

After compiling you need to put your new kernel in lilo or grub. For the older kernels there is always a line with a vmlinuz-kernelversion.img file in it. What is that file? Do you have to create such a file for the new kernel or can the same file be used?

i'm not really sure what file you actually mean. the kernel itself (e.g. /usr/src/linux/arch/i386/boot/bzImage --> /boot/vmlinuz-2.4.18) or the ramdisk image (/boot/initrd-2.4.18.img)? if it's the latter then you don't normally *need* a ramdisk to boot, but you can create yours using mkinitrd.

yes copy bzImage to /boot
and make an entry in lilo.conf or grub.conf (depends which one are you using)
all you need to change is image file entry where you put your new filename
and if lilo run
lilo
if grub you're all set

sorry if grub, make sure to put it as default image if you wanted to have it as default