Microsoft has decided to not to release any future update of Service Pack 2 for its most successful windows till now Windows Xp. From 13 July 2010, no future security fix will be available for Win XP Service pack2. However, for other versions of Windows xp, the updates would be continuously releasing in the future. Along with Windows XP service pack 2, Microsoft has also decided to diminish the Vista updates from 13 April, 2010. No doubt, Vista failed to get as much recognition in the market as Microsoft predicted. Microsoft will discontinue vista’s security fixes also.

How to know which OS version you are running
If you are using Windows XP, follow these steps:
Click Start–>Run and type winver and press Enter key.
The below image shows your Version Information:

For Windows Vista, do as follows:
Click Start button and type winver in the search box and press Enter key.
You will get an image as below:

So, if you are using any of the above 2 OS, switch to any other OS if you want future fixes of your operating system. If you are using Service pack 2 or vista and are happy with the current releases and can reject this Microsoft’s warning, you can continue with as usual.

You can read more this at Microsoft’s website at End of support for Windows XP and Vista