Turn off autocorrect

Hey all, i haven't been on here in awhile, and the new UI upgrades look nice. I am currently Lion, unfortunately, and I am starting to get annoyed with the stupid autocorrect feature. Whenever i type in acronyms, it changes to something else unrelated, and for some reason, it tells me words are wrong when they clearly aren't. For example, I'm testing a program called FWi, and when i write about it, it gets changed to Fwi, and each time i go back and change it, it reverts. Then for the other example, words like won't and couldn't, the won and could get underlines as being wrong. Now i did try to disable the autocorrect by going into Prefs/Language and Text/Text and deselecting its option, but that hasn't seemed to have done it. Is there anything else i'm missing? Thanks