As has been noted in repeatedly in both comments and in other answers, you CANNOT install IE6 in Windows 7. Doesn't work. Don't even try, Don't waste your time. Even IF you could get IE 9 off this system, all you'd get would be IE 8 (that's what comes by default in Win7), and that CANNOT be uninstalled.
While some have suggested the complicated route of using virtualization, (which may be a good plan B, start at the very least with a much simpler plan A, compatibility mode)
A. Rather than trying to remove IE9 (which is NOT recommended) and trying to get some archaic browser installed, use compatibility mode. Simply press F12 in Internet Explorer at anytime.
![Compatibility Mode Menu]
Compatibility Mode will allow you make IE render pages as if they're an older version. They're like "Jedi Mind Tricks". It'll trick the website into thinking you're using an older version.
B. Try XP Mode in Win7. This little known FREE add-on to Win7 lets you run XP inside Windows 7.
It's the best of both worlds: The new Windows XP Mode lets you run older Windows XP business software right on your Windows 7 desktop.
I would say compatibility mode is a better route, it is a lot easier, and If I had to guess, most likely to work, but I also know XP Mode may also do the trick. XP Mode may take some more time, but it's guaranteed to work, it's a free VM for XP Microsoft lets 7 users download.