You can use

overflow: auto;

to allow a scroll bar to appear when a "word" in the text is too wide to fit. You might not like the look of this, but it is a possibility.

There is another property which one of my references says is non-standard and supported in IE5.5+ only, but works now in Firefox 3.6:

word-wrap: break-word;

I don't know what other browsers may support this, but if FF and IE do (and it doesn't blow up other browsers) that is enough market share to be worthwhile.