Installing an older program in Windows 7 using Windows XP Mode is not that different from installing it in Windows XP itself; you just need to install the program from within the Windows XP Mode window. But once it's installed, you can access the program from anywhere in Windows 7. The ability for Windows 7 to work seamlessly with your older Windows XP programs is one of the key enhancements of Windows Virtual PC.
Before you can begin, you'll need to have both Windows Virtual PC and Windows XP mode installed. You can use this same process to install applications within any virtual machine.
Choose Start→All Programs→Windows Virtual PC and then select Windows XP Mode.
Maximize the Windows XP Mode window so that you are in full-screen mode.
Notice the toolbar across the top of the window.
Choose Start→My Computer and then locate the program that you want to install.
If the program you want to install is on a USB device, you'll need to attach the USB device to Windows XP Mode before you can access the file. Click the USB tab at the top of the screen and select the device you want to use.
Double click the application file and follow the on-screen prompts.
Each application will use a slightly different installer, but the basics will be the same.
When you get to installer page that asks you to select the location for the application, be sure to select that you want the application accessible to Everyone.
This option will enable the program to be accessible in Windows 7.
Click Next as necessary to complete the installation and then close all open windows, including Windows XP Mode.
If you used a USB device to load your program, you'll want to release it before you close Windows XP Mode so that the USB device will be accessible to Windows 7 again. Click the USB tab at the top of the screen and select the release option.
Locate the new program on the Windows 7 Start menu.
Under Windows XP Mode, you'll see a folder called Windows XP Mode Applications that contains any applications you've installed there.
If you plan to use the application frequently, you can right-click it in the menu and choose Pin to Start Menu or drag the program's icon from the menu to the taskbar.