After some research on the subject, so far all I have come up with is that you can't, if you are limited to standard Access text boxes. They can handle ordinary text or RTF, but not HTML - as far as I could find. The only suggestion was to see if you could find a third-party set of specialized controls compatible with Access but that included HTML interpretation.
Short answer: Without spending money for third-party tools or using free-ware code of questionable reliability - you can't.