Internet Explorer 6.0 is now, due to it's age, an absolute piece of crap. There was a time that I actually LIKED IE 6.0...mostly because I wasn't doing deep level web development at the time. Back in 2003, it was great! Now, it's 2009. IE6 was 2 years old IN 2003. Why the heck are over 15% of users STILL using IE6? Often, these are the same people who are clinging onto Windows XP for dear life, like their computing days will be over if they have to use the dreaded Windows Vista. Internet Explorer 6 was the included browser in Windows XP for it's entire life.
Internet Explorer is a thorn in ALL web developer's sides. In reality, most would ignore it's idiosyncrasies and inabilities to render CSS in any way near the W3C standard, if it weren't included in the Operating System with the largest installed user base out there (Windows XP, as of this writing (June 2009) STILL has 61.54% market share of ALL operating systems, including Mac OS X, etc), I doubt it would be the market leader.
IE has been catered to for years. It's ActiveX controls are nice, especially on some interactive web sites. They have also been the source of the most trouble with spyware, hacking, etc, and have had numerous security fixes (hundreds) over the years.
Honestly, my biggest gripe is that the CSS support is so pitiful. You have to walk on eggshells and use non-standard code often just so it will render somewhat like it should in browsers that are more standards-compliant, such as Mozilla based browsers like Firefox, Netscape, and Flock, as well as Apple Safari.
So, I suggest that you upgrade to Firefox, Opera, or Safari today. At the very least, upgrade to Internet Explorer 8. While it still has a few quirks, it's substancially better than IE6 is in the realm of CSS Standards support. Do us all a favor, though, and try NOT to run it in compatability mode unless you absolutely have to.