As of the recently released version 50 of the very popular Google Chrome browser, Microsoft's ancient "Windows XP" operating system is no longer supported.
While Microsoft ended support for Windows XP over a year ago, there are still a number of people using it. With Google now no longer supporting the OS, this leave just Firefox of the big 3 browsers as "relatively safe" to use within XP. However, Firefox will also soon not be supported.
If upgrading to Windows 10 (or 7, at a push) is completely out of the question, our advice would be to entirely isolate a Windows XP machine on your network. Ideally, it should have no internet access at all. If this isn't possible, ensure that the machine doesn't have access to any of your networked files beyond those that are absolutely essential. A Windows XP machine on a company network at this point is a very easy way for any number of attacks to be launched (including various forms of ransomware that will encrypt all files it has access to - not necessarily just those on the machine itself).
As for Chrome, along with XP, support has also now been dropped for Windows Vista, OS X 10.6, OS X 10.7, and OS X 10.8.