How to keep security level after OS or DB would be expired

Hello Experts,

Our SAP system runs on WIndows2003.

And it is very difficult for us to upgrade OS to WIndows2008.

But Windows2003 patch would not be provided after 2015,

because Windwos2003 maintenance be finished.

Therefore I'm looking for the way how to keep security level somehow...

Unfortunately, until now I don't have no idea!

If someone have same or similar case, please tell me the information.

Jus hint would be usefull for me.

Thank you for advace.

Best Regards.

Toshi