Dashboard Widget for Mac OS X

I need to create a dashboard widget that will output Growl notifications when a member on a website goes online. The status of a member changes when he/she logs in and out of the website. It will be similar to the Delivery Status widget ( [login to view URL] ) but instead of tracking parcels, it will track the status of members on a website. Here are the details: 1- User can choose which members to follow 2- The widget constantly checks for the status of the members 3- If a member goes online, a growl notification is sent to the user Note: I already have PHP code that returns the status of a certain member.