Natural Weather is buggy, and Natural Vegetation is made obsolete by a newer, better alternative. I recommend Weather: All Natural, but HTF has updated Atmospheric Weather System (AWS), and Enhanced Weather (EW) has been updated too!
http://sites.google.com/site/oblivionpoinfo/downloadmods <-- links to the four most popular weather mods toward the bottom
http://sites.google.com/site/oblivionpoinfo/stabilization/outdatedmods <-- with suggested alternatives
Edit: Get the latest version of OBSE v18 stable. It is not prone to crashing. However, a mod that uses it might be prone to crashing, as well as bad configurations made by the users (i.e., incorrect installation and load ordering.)