This is a small demonstration of dynamic positioning. It should work in all (DOM enabled) browsers. Note, that Opera requires the fixed postitioning up to version 6.03.
Nonetheless, it is wise to use absolute positioning, since this doesn't cause ugly reflows.
Above, there's an example paragraph that you should hover. Follow its instructions :).
This is not a complete example but should demonstrate the way to do it.
Just take a look at the source