Newline in a guestbook

Hey guys! I'm writing a guestbook with mysql. My probblem is that when user enter at long word like blablablablablablablablablablablabla my html-tables gets screwed up. If someone is just fooling around the whole page design can be destroyed. I want to know how I can make sure that no word is longer than x characters. If a word should be longer than that, I would like the word divided into smaller parts with a - character at the end of the first word like this: "this is a text in the guestbook. if there is a really long word like blablablablablablablabla- blablabla it is divided into smaller parts and a - char is added to the first word." I thought about reading the whole message into an array, and then loop through it and for each word check whether it is larger than x chars, and if so, change it. But couldn't that be a very memory consuming script if it should do that for every message? Anyone knows how I could do this?