Which versions of IE should I still support?

I design a web site for a small dance group based in CT. I've had problems getting transparent PNGs to work in IE 6 and earlier. I fixed some of them, but I can't fix PNGs from CSS files. So I would have to re-write the entire site to make it work. That's really not an option.

So... is it safe to tell users that are running something earlier than IE6 that they need to upgrade their browser? I looked at this chart on Wikipedia and it says that IE6 is supported on all versions of Windows since Windows 98, even though tech support has been dropped for it. That means that any version of Windows released in the last 10 years can run IE6.


I haven't realized until now how much I hate Internet Explorer!

Edit: Just to clarify, the users that are using something before IE6 would see a screen that tells them to upgrade their browser, but also gives them the choice of a) using the old, outdated site, or b) using the new, broken site, and emphasizing that their browser just doesn't work with the new site.

 

OK. I set it up to work like this. Do you think this is OK?

The normal site works fine in everything but IE6 and older.

Anything but IE - normal site.
IE7 and newer - normal site.
IE6 - site without PNGs (using a different CSS)
IE5 and older - tells users to upgrade their browsers, visit the old site, or use the broken new site.

 

Or at least 99% of the time.

Here's the non-IE and IE versions of the site. Do you think that the IE version looks OK?

Non-IE: http://zolotyjpromin.mikenetic.com/new/index1.php

IE: http://zolotyjpromin.mikenetic.com/new/index1.php?forceie=true

And I just checked our stats, which I forgot that we have, and with our old site 38% of our users were using IE6 and less than 2% combined were using IE 5 or IE4. The remaining 60% are using something that doesn't suck (including IE7).