To supplement what Malicious said, no one else does that trick like SuSe, but that's pretty nifty... I'm glad I'm downloading the Suse 7.3 Sparc ISO right now.
Also, I think that the default kernel source install is going to have all of the compiled source present, therefore you will have to run a make clean in order to have everything come out right. If you 'make mrpropper', it will wipe your config file. You can always save this config file elsewhere and then move it back.
The other pain about a mandrake kernel re-compile is that Mandy uses the alsa sound modules, therefore you'll have to recompile alsa again after the kernel compile in order to get sound back. They're in /usr/src/linux with the rest of it, but don't get compiled with the kernel.
Why, offhand, are you re-compiling the kernel?