As you read in the title, I passed to Windows 7 from Xp...I kept all the content of the Morrowind folder but when I tried to open it says that d3dx9_30.dll is missing. Now, do I have to reinstall Morrowind and, if so, is there a way to keep all my mods, texures and meshes?

Ty, guys

You probably need http://www.softpedia.com/get/System/OS-Enhancements/DirectX-9.0c-Redistributable.shtml and check the http://www.gamesas.com/index.php?/topic/1117223-morrowind-graphics-extender-mge/ thread.

All your mod files are in your Data Files folder. Set it aside so that it doesn't get deleted when you erase all your MW files.
But you shouldn;t need to reinstall anyways