make mrproper

Then copy your existing .config to your new kernel source tree...

cp /usr/src/linux-2.4.?/.config /usr/src/linux

make oldconfig (to use your old config and choose to add/not add the new options)
or...
make menuconfig (to use your old config and tweak further)
or...
make whatever other type you like (xconfig,gconfig,etc.)

Just exit and save the configuration, then...

make
su -c "make modules_install"
make install