I'm trying to get a DIV, and after 2 seconds start fading it (setting its opacity increasingly lower). When it's totally faded, I will remove the innerHTML of the element leaving it empty

The code I'm currently using works only on firefox, and it's this

Now onto the tricky question
I know from my CSS lore that the corresponding IE style to get 50% opacity is:
filter: alpha(opacity=50); (instead of FF's opacity:0.5)

How can I use this to insert a second setTimeout for IE's opacity?
(similar to setTimeout("c=setInterval('document.getElementById(\""+id+"\").style.opacity-=0.025',25)",2000);
I would ideally need to decrease by 2.5, every 50 milliseconds, the value in filter: alpha(opacity=50);