I need minecraft help! please!?

ive been having problems with minecraft, the game itself runs fine. but i cant use mods ors texture packs. i had to down load mcpatcher just to get the texture pack to load, but then the game crashed whenever i tried to place a block. and idek how to download a mod (like i really want the nuke one) some help? im thinking of just uninstalling the client then reinstalling, but idkwhere to find the save files to extract them so i dont lose my world and all my progress. some help would be most appreciated!