Come July 14 2015, Windows server 2003 will no longer be supported and will not receive patches and updates. If your business is still running this software, then Geidi strongly recommends upgrading as continuing to run server 2003 is a risk for your business.
Why is it a risk?
The main reason is that security holes and exploits are constantly being found in all forms of software. When they are patched, the risk goes away, or is at least greatly reduced. When updates and patches stop, these security holes remain open for the whole time that you continue to use the software leaving your business extremely vunerable to hackers.
Techradar calls the End Of Life for Server 2003 the "biggest security threat of 2015". Considering the number of serious exploits identified this year, that's really saying something! You can read more on their site here.