If you’re using different style sheets, you’re going to get different results.
And I’m surprised you say IE looks right, since any IE less than 7 doesn’t do PNG correctly. I put in a GIF override in the iestyles.css for my logo just yesterday.
But (snief) I can’t found it.
If you add the .png HTC fix or doublehelix fix, i can’t remember the URL but google will have loads of hits for it. Just add to CSS rule to each selector that will contain a transparent .PNG file and you covered for IE6 and up. In regards to the outer glow effect, try exporting it through fireworks as that has the best colour palette control for .PNG’s