I started using NetBeans and quickly encountered the annoying red underlining of all words in my code. Disabling the spellchecker feature in NetBeans 6.9 is NOT done by deselecting all files in the Options -> Miscellaneous -> 'Spellchecker' tab.
For NetBeans to really understand that you don't want spellchecker, do the following:
Go to Tools -> Plugins -> Installed tab -> select the spellchecker plugin -> press Deactivate -> restart NetBeans
Alternatively try adding the file type you are working on (if NetBeans doesn't recognize it) by following this post: http://www.herikstad.net/2010/07/filetypes-in-netbeans.html#links