Windows 7 Professional, Enterprise, and Ultimate gives you something called XP Mode which is a free XP Professional that you can download from Microsoft’s site.

One issue if you have a machine with a lot of RAM, you may find it slow but can speed it up increasing the amount the virtual machine uses.

You will need to install an antivirus program inside of Virtual XP. You will install whatever programs you need to install also inside this as well. If a program runs fine in Windows 7, then just run it in Windows 7. This is for programs where you have to have XP or a 32-bit OS if you have 64-bit Windows 7.