Windows XP with Serivce Pack 1 is no longer publicly supported by Microsoft as of October 10th, 2006. Microsoft will not issue bug fixes nor security updates for this level of the operating system. To continue support, you should deploy Service Pack 2 for Windows XP. You can find more details here.
There was a considerable amount of concern about deploying Service Pack 2. A lot of people were scared that the new Windows Firewall would break their networks. By default it was turned on but anyone who did some research would have found they could control it centrally with either registry edits or Active Directory Group Policy.
Other concerns were raised about the increased level of security in the subsystem. This caused some fear and rightly would have required regression testing for all business applications. Another complicating factor was that many vendors acted as if Service Pack 2 was sprung on the world by surprise. Companies such as SAP were allegedly slow to support the service pack for their products. Of course, Microsoft had a substantial publicity and public beta program building up to the release of Windows XP Service Pack 2 that gave these vendors absolutely no excuses.
Given that Service Pack 2 for Windows 2003 is on the way, I’d recommend you make sure all of your Windows 2003 servers are upgraded to Service Pack 1 and not give your vendors any room to wiggle out of their responsibilities.