If the discs function on Windows XP, why not just use them on Windows XP? Under Vista, 7, or 8.x, you can create what is known as a virtual machine, which can easily run older copies of Windows, provided you have a license to run them of course, and you can run older software on the virtual machine when you can't otherwise get it to function with new versions of Windows. The caveat is that you usually do not have advanced hardware functions such as 3D support from the graphics card, but often times the older software doesn't need such support.
For Windows 7 through XP, Microsoft provides free of charge, Virtual PC, and for Windows 8.x, virtualization is built in to the OS and no extra software is needed.
Virtual PC can be found here:
http://www.microsoft.com/en-us/download/details.aspx?id=4580
Once you have created a virtual machine, you can install any supported operating system that you have a license for, and should even be able to install Windows 98 to support your particular software you are concerned about loosing.
If you are concerned with the lack of new security updates for XP after next month, you can disable the network interface of the virtual machine, and it will not be susceptible to threats from online, as it won't be online without networking, although the host machine will still need proper security in place.