Unfortunately, it’s sort of a pain. If you have an intel Mac, things like bootcamp, crossover mac, parallels, and fusion are your best bet, though they all require some overhead and annoyance (and only bootcamp is free). But they will work.
If you have a PPC mac, there is a very slow roundabout method using Virtual PC, but I’d recommend against it, as it’s horribly slow and a pain to setup. There also is a way using Wine and some linux stuff that’s free, but it may require serious tinkering (this may also be Intel only).
Your memory is correct about IE on mac, but this is actually of no use, because is a terrible and discontinued product, and bares little resemblance to IE on a PC.
I’d recommend this awesome screenshot site where you can get IE screenshots over the web, but they may be insufficient, depending on your needs (because there’s no interactivity). I find it very handy: http://ipinfo.info/netrenderer/index.php
Finally, you may find it worthwhile to invest a few hundred bucks in a crappy windows machine from craigslist, and there you can test everything with maximum authenticity.