If your company is still running Windows 2000 or Windows XP SP2, you only have a few months before Microsoft retires support for those operating systems. And beginning in April, there will be no more security updates for the RTM version of Vista (the original release).
It's time to upgrade your XP machines to SP3 or start planning to switch to Windows 7, if only for the security advantages. And those Vista computers need to be upgraded to SP1 or SP2. Statistics show that the newer versions of the OS have fewer security vulnerabilities than their older counterparts.