As you've probably already heard, there's a dangerous vulnerability in Internet Explorer 6 & Internet Explorer 7 being exploited in the wild. The vulnerability affects Windows XP Service Pack 0 to Service Pack 3. Microsoft hasn't released a patch yet, but they have provided a work-around.
The vulnerability allows arbitrary code execution and we therefore strongly recommend that you should apply the workaround from Microsoft's advisory or turn off ActiveX altogether. Otherwise you will be at risk of exploitation of Internet Explorer 6 and Internet Explorer 7.
(08.07, 15.04: edited to correct typo in the Service Pack information.)