There’s no sane reason not to use 24bit PNG for all layout image needs given the abundance of low cost storage and super broadband. I ignore dialup users: they have no business using the interweb. They’re too cheap for pay for appropriate access ergo they’re unlikely to buy whatever you’re selling.

24bit PNG also provides 8bit transparency vs 1bit transparency of GIF (which is itself limited to 256 colors.. yuck). Animation? Not GIF: use flash until the firefox oligarchy realizes the awesomeness of MNG.

Onto the crux..

We’ve been using sleight.js to enable microsoft’s backwards-, non-standards-compliant web ‘browser’ to function less poorly. Here’s a more recent incarnation:

http://allinthehead.com/retro/289/sleight-update-alpha-png-backgrounds-in-ie

Depending on your interweb needs another fantastic option is to take the opportunity to motivate the unwashed masses to escape from IE tyranny to Firefox freedom via creative mod_rewrite directives. The fewer people suffering with IE on your site the less time you have to WASTE catering to cretins.