May I suggest that instead of downloading a database you calculate the "did you mean" on the fly?
You can use soundex, metaphone, or similar concepts.
What you will need is your language database of words, and the selected phonetic algorithm results.
Since this is for your web site, you can even create this through a program, and periodically update it.
This would allow you to create the "did you mean" results, on the fly.
That is, let's presume you select soundex as the algorithm.
* Go through all pages of your site and create database of words and soundex (filter non-relevant pages, duplicates, stop words, etc.)
* Primary key would be the soundex.
* user enters "helllo".
* Calculate soundex.
* look up matching soundex in DB.
* display words as "did you mean" with appropriate links to pages...
edit: eh, Demaestro already said while I was typing it up. :D
[edited by: Tapolyai at 7:40 pm (utc) on Dec. 6, 2007]