1. Well, if you installed it as an RPM then you can uninstall it using rpm -e (or using RpmDrake in the Mandrake Control Center). Otherwise, look at the instructions you used to install it.
3. Use Mandrake Control Center (MenuDrake)
4. Keep using it, maybe try a different distro (Gentoo is great for learning the mechanics of it, or even Linux From Scratch to really get your hands dirty); maybe buy a book (make sure you get one written recently); build a router, a web server, a print server running Linux or a BSD; compile your own kernel; there's loads you can do - have fun!