I hear this as a issue for a lot of companies. Yes Microsoft has some great products for virtualizing old applications, But here some special. UniBrows is a add on for IE8 or IE9 that add a Tab in your browser that allow you to run IE-6 dependent web application unmodified in IE8 or IE9.
This solution work for those customers who need JUST browser backward compatibility. The cool thing about this add-on is that now you can migrate to Windows 7 easily.
You can even had different version of Java running in your browser!
For a Trial Version go Here