I use a minimum search term length of 2 in my forum.
A post containing the sentence

"This is new in Photoshop CS3"

will be found when I search for

"Photoshop CS3"

but not when I search for

"CS3"

Is this the intended behavior?

EDIT: If you're having this issue and running the latest version of UBB, you can switch the search method to internal and you'll be able to search for 3 character words.