You should have taken the recent Sitepoint CSS3 Live course as these issue were covered in detail in the course
Make sure that you code so that IE6 - 8 (and others) are fully functional first then add your enhancements for better browsers afterwards. Don't do the reverse.
Use only properties that aren't critical to the design so that if they are not working in one browser it won't make much difference.
e.g. things like border radius can be added and IE just gets square corners as before but still remains fully usable.
If you are using html5 then you need to add support for IE (and make sure you set the new elements to display:block).
You can find some useful css3 tools at John Allsopps site here.