It is always something isn't it! You did not need to do what you did, and extricating yourself will take a little work on your part. Buy, hey. Its what *I* did, too, and learned from it.
Now you will have to rebuild your kernel (UGH!). In the /usr/src/linux-2.4/ directory, you'll find a file called .config. If you don't see it, you'll find it in /boot but it will be named .config-2.4.20 (or something like that). If you don't find it in either place, then you will find several (get the right one!!) in /usr/src/linux-2.4/configs/ Copy that file to your home directory (this is important!), or to root's home directory. You can't recover with out it! So save it.
Now then, make sure that you are root and in /usr/src/linux-2.4
(make mrproper will delete any file in /usr/src/linux-2.4 that starts with .config, that's why you copied it to a safe place.)
Now copy the config file back to /usr/src/linux-2.4 and be sure it is named .config
Then do this
If you had no errors, then reboot.
You should see your "custom" kernel in the GRUB boot screen. Choose it before GRUB chooses something else.
Rebuild your NVidia driver. And you should be good to go.
If you want to change things so your custom kernel becomes the default boot kernel or you want to get rid of the word "custom" in your kernel, just repost and we can walk through that.