I think you should upgrade to IE6 regardless. It's only time before you MUST do the upgrade.
I've IE6, and once in a while, I get the X in the picture (esp in this board). When I refresh, the picture comes back. I think it may have to do with the speed of the host server too. Meaning, if the server that hosts the pictures / icons is a slightly slower server, then it may not catch up as well with your speed of your DSL. I dont' think it has much to do with the browser.