I found a project that does allow a web interface to the vacation program. The webmin project, www.webmin.com,
To allow your users to update their own vacation information you need to also install the usermin program and the usermin vacation module.
I also installed a vacation module in the Webmin application so that managers can enter a vaction message for employees that are sick.
This application also gives windows users a web interface that can be used to change their password on the Linux server.
I spent a lot of time searching for this, so hopefully this message will be indexed to make it easier on the next person who needs these abilities will be able to find it faster than I did.