Windows XP Service Pack 2 only appears in Add/Remove programs for machines that were originally on SP1 then upgraded to SP2, so the default K1000 appliance Software inventory for this item will not reflect machines that are already on SP2 because they were originally imaged at the SP2 level.
When using the K1000 appliance to deploy Windows XP Service Pack 2, you should use the following custom inventory rule for the Software Inventory item:
RegistryValueEquals(HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion,CSDVersion,Service Pack 2)
This custom inventory rule will prevent the K1000 appliance from trying to deploy the SP2 install to any machines already at that level (i.e, SP1 machines which have been upgraded, as well as machines originally imaged with SP2)