Hi obayda. First of all you might like to check out the tutes on my Lair. Link in my sig below. Use the CFS2 Scenery Clinic for installing scenery as it's basically the same & I didn't do one for FS2000. If you're using WinXP you won't need WinZip. As you've installed repaints you obviously already know how to extract zipfiles.

PS. If you're still not sure on anything please don't be afraid to ask. When in doubt refer to the default aircraft. Good luck.