there's a hotfix available from a 3rd party, several highly reputable sites are recommending to install it, especially if you use IE for browsing.
read about and download it here:
http://www.grc.com/sn/notes-020.htm
looks like 2000/xp are only vulnerable OS's for now, but that could change, w9x should also be vulnerable from what ive heard. all it takes is looking at the graphic file in IE, supposedly opera and firefox will prompt you before opening. also, if you use google desktop search or msn desktop search, just having it on your hdd and being indexed will trigger the exploit. sounds like a nasty one
