The database that was formerly provided by dejanews - and later deja.com - has been acquired
by Google. The "Current" and "Old" archives have been combined and extended,
now going back as far as 1981.
The Google Groups main page is good for text searches of all newsgroups.
The Advanced Groups Search page allows you to
specify additional criteria such as newsgroup, subject, author, and message date.
If you want a text search of alt.usage.english only, try the alt.usage.english page - all you have to do is to enter the text and click on Search only in alt.usage.english.