Dynamic Updates

I need to know if I should use asp.net or Java for this. I would like to use asp in general. I need to have a function check to see if a variable is true or false and update an icon. But I want it to either check when updated or every 3 seconds. I suppose it has to be somewhat client side scripting but is there a way around this.

As of now I use IFrames whith a refresh of 10 seconds, any less will cause it to timeout. I kind of want it real-time or very near. It's kind of like a status page for information in a database.