You should be able to cd to /usr/src/linux and look at a file called .config. You should be able to copy your existing kernel config by doing the following:

cd to 2.4.18 kernel source (say /usr/src/linux-2.4.18)
make mrproper
cp /usr/src/linux/.config ./
make oldconfig <-- this is similar to make menuconfig, except you will only be prompted for items marked NEW.
make
etc..