ASP Classic Regex Replace - Simple project

I would like a simple replace function in ASP that replaces text in a string BUT skips any links in the string (ie. any <a href>..<a> tags) function should replace first occurance only. It should take in three arguments content, oldstring, newstring and be efficent as it needs to be run a number of times (ie. only create one regex object if required). It should only replace text if there is alphanumeric no characters on either side of the string