While no option is perfect, there are a few choices:
1.) Adobe has a SVG plugin for IE8 http://www.iegallery.com/en/addons/detail.aspx?id=444
2.) The Raphael JavaScript Framework allows vector graphics cross browser – http://raphaeljs.com/
3.) Then there are the Open Source projects: http://code.google.com/p/svg2vml/ and http://code.google.com/p/svgweb/
4.) There is the option to display flash for IE8 and below.
5.) There is the option to gracefully degrade for IE8 and below and show a static image in place of the animation.
Based on your reason for the animation – I would recomend 4 or 5.