Yikes. Okay, well is there any way I could allow a 3 character search? What about if I use the "built in default search"?

u can switch it back to the vb search and set the limit in the admincp as suggested above by banana.

If you know that you'll only have a limited number of three letter words that users would search for, you can put them in the "Words to be Included Despite Character Limit" field. That way your board won't index common words such as "the, for, way, you, can, put, not, fix, yes, and" and so on.

Is there some sort of a hack to get round this?

What do you mean? If you're using the default vB search, you just have to put the three-letter words that you want added to the search index into the field that I mentioned, "Words to be Included Despite Character Limit".

For instance, I run an automotive/offroad forum, so I have things like O2, ATV, ABS, and fan included in the search database while my minimum character limit is set to 4 characters. So those words are still able to be searched for even though my limit is 4. No hack necessary.