1-You can choose the kernel you want... personnally I would download kernel sources from
kernel.org but if you prefer recompiling mandrake kernel sources....
to patch a kernel, that's very simple:
-download the patch
-then:
Code:
cd /usr/src/linux
patch -Np1 -i ../path/to/my/patch.txt
and that's done
2-about /boot partition, I think it's about 50/100 mega large (type "df" in a console to know it)... In fact, to add a new kernel and its symbol table (the System.map file), you need 2Megas if you don't put too many useless features in your kernel (currently: my 2.4.28 compressed kernel + my System.map = 1264Ko).
When you finish kernel compilation, it will generate a file called bzImage (in relation with the make bzImage step)... this file is located in /usr/src/linux/arch/i386/boot/... and you need to copy it in /boot and also rename it as vmlinuz (in fact you can rename it as you want but many people rename it like that)

you need to configure lilo yourself... have a look in /etc/lilo.conf (I think you'll quickly understand base config)... once this file modified you need to run lilo, for that just type "lilo" in a console... If you make a mistake in the config file you'll be warned and you'll be able to correct it and re-run lilo
Hope I've correctly shed your lights
Oliv'