Windows XP is probably one of the best Windows OS that they have made. Many high end proprietary systems still use it as the base for their systems. The TV station that I just retired from just spent several million dollars on state of the art automation system to run the 5 networks that came out of that building. The computer systems that ran the system we found out was running Windows XP.
That being said it is time to upgrade. Modern software is now being rewritten to take advantage of the new OS and many companies are dropping backward compatibility since trying to do that made the programs buggy and bloated. Just handling the latest couple of OS makes the programs much better and also cuts the cost or at least gives them more profit.
Very good desktop systems running Windows 8 can be had for $600 to $700 that will run all the latest and greatest program.