Question: We've got some fraction information stored in the database, e.g. ¾ ½

Short of doing a search and replace, are there any inbuilt PHP functions that will automatically convert these to proper html entities?

Answer: 
You can use the [htmlentities() function](http://us3.php.net/htmlentities). This will replace all special characters with their HTML equivalent. It should do the job.
try htmlentities()