ASP.NET - Comet Pushing messages from server to all clients

I'm making an application with server sided variables that change every second. Every second those new variable need to be shown at all the clients that have the webpage open.

Now most people told me to go with comet because I need to push/pull the data every second, now I've got a few questions:

• What would be a better solution looking at the fact that I need the new data EVERY SECOND, pulling from the client or pushing with the server?

• Also the item ID's that are on the server side (with the variable's that ID got) can change and when the client refreshes the page he needs to get the oldest (and living) ID's. This would mean that my jquery/javascript on the client side must know which ID's he got on the page, what is best way to do this?

• Last thing is that I can't find a good (not to expensive) comet library/api for asp.net (C#). Anyone ever used a comet library with good results? We're looking at a site that should be able to have 2000 comet connections at every moment.