There is a series of articles by Randall Schwartz that deal with methods for updating web pages dynamically. You might be able to adapt one of these methods to your problem:

http://www.stonehenge.com/merlyn/WebTechniques/col17.html
http://www.stonehenge.com/merlyn/WebTechniques/col19.html
http://www.stonehenge.com/merlyn/WebTechniques/col20.html