vim tips and tricks
This is a good place to learn about plugins. Go to www.vim.org, click on the Search link, search the scripts for spelling, and then download the vimspell.vim plugin. To install it, put it in your ~/.vim/plugin directory. Then vim a file and type :help vimspell.
The page on word completion also shows how to load a dictionary. You probably want to put the :set dictionary=/usr/share/dict/words in your .vimrc file.