I was, today, going to make an addition to my post about the same thing. Though, to be honest, I was going to suggest Windows 8 rather than Linux. So, here goes.
Lynn, you already own copies of XP, and their Product Keys should be on a sticker on the XP computer cases. That's all you need for this next little example. If you don't have the actual Windows XP installation CD, don't worry. There's lots of places on line where you can download an ISO, or the installation files, to burn yourself an installation CD. It's the Product Keys, which you already have, that will make this project a success.
For this example get yourself some copies of Windows 8.1. Any version will do, you just want them to run on your computers.
1. Backup all your data. I should have said that in the Windows 7 example, but I forgot. Don't you forget.
2. Install Windows 8.1 (from now on when I wright Windows 8, I mean 8.1), formatting your hard drive to give it a nice fresh environment to install to.
3. Jump on Windows Update, again, and again, until you have every last update there is.
4. Download, and install Classic Shell For Win 8 to give you a true Start Menu for Windows 8, and a few other enhancements. You can find it at: http://www.classicshell.net/ .
5. Go to ORACLE's VirtualBox Web Site: https://www.virtualbox.org/, and download the VirtualBox platform package for Windows, VirtualBox 4.3.14 for Windows hosts x86/amd64. Don't worry about the amd64, it works on the Intel chip just as well. Save it in your Downloads directory.
6. Now download VirtualBox 4.3.14 Oracle VM VirtualBox Extension Pack. Save it in your Downloads directory too.
7. A bit farther down the page you will see User Manual. Click on that (NOT the HTML version) to open it, then save it to your Downloads directory as well. We just want everything in one easy to find place.
8. This would be a good time to download, and install the Adobe reader, if it's not preinstalled in your copy of Windows 8.
9. Now open the User Manual in your Adobe reader, and read up on setting up a Virtual Machine. Don't worry, it's not difficult to do. Just give the User Manual a good read for the first few chapters. We want you to be comfortable doing this, and the knowledge you gain from the Manual will make you comfortable.
10. Install the VirtualBox software like you would any other application. If you're new to Windows 8, and you are, I think you would be more comfortable installing it form the desktop rather than the Start Page. If you have all the updates done on Windows 8, you can skip the Start Page altogether if you want. Instructions are available on line, in various help sites.
11. When you have VirtualBox installed, it's time to install XP, and set up its Virtual Machine. With VirtualBox open, and running, click on the "New" button at the top of the VirtualBox Manager window. A Wizard will pop open to guide you through setting up a new Virtual Machine. From that point on, just follow the wizards, until XP is installed, and running.
As you're using the same computers, with the same RAM as you were using for XP, I would allocate as much RAM as you can to your Virtual Machine. If your computes aren't maxed out on RAM, I would think about adding some more.
When you get to what kind of Virtual Disk you want in the Wizard, I would go with a dynamically allocated file. That's the same type that would be created in the Windows 7 example, and though marginally slower than a fixed-size file it lets you work away in XP, and still have some room to play with Windows 8.
At this point in the process you will get a second Wizard. The First Start Wizard will help you install XP in your newly created Virtual Machine. This will entail you putting your XP installation CD in your optical drive, and telling the Wizard where it is, by using a drop down list.
Now it's just a matter of following XP's installation instructions. This is where your Product Keys come into play, you will need them to install XP. Fortunately, they should be on a sticker on your computers case. On my Dell it's on the top, but every manufacturer puts it in a different place. If it's not on the computers case, look on the CD case, or envelope, or box if you bought it retail.
12. Now that you have XP installed in its Virtual Machine, and run Windows Update to bring it back to the last of the updates, then close off its internet connection permanently. You can now start restoring your data from the back up you made at the beginning of this process.
13. When all your programs, and data files have been restored, you can go back to working in XP to your heart's content.
14. Install your Antivirus software, and connect with the internet with Windows 8, keeping your XP isolated from the outside world, and there for safe. If, while working in XP, you need to go on line for some reason, minimize your XP window (if your using XP in full screen), and go on line with Windows 8. You can copy, and paste between the two Operating Systems, and if you have installed the Extension Pack, and VBoxGuestAdditions, your XP will have access to Windows 8's drive.
Now, this setup is not as seamless as XP Mode on Windows 7, you can't run XP programs from the Windows 8 desk top, but it is the easiest way to get your XP specific software to run on Windows 8. It will also give you a lot more breathing space to run XP before Windows 8 reaches its inevitable end of live. You can also use this exact same setup on Windows 9 when it is released.
This gives you another option to keep your XP up and running. I hope it helped.