If you want to realize dual boot Windows 7 and XP under XP, you just need first install Xp and then shrink your hard drive to recreate a primary partition, and then install your Windows 7 on it. That’s OK. But if you want to realize dual boot under Windows 7, it’s a little hard.
First you need to prepare Windows 7 installation disc and Windows XP installation disc.
Step1. Under the Windows 7 OS, shrink your hard drive and create a primary partition for XP.
Step2. Start your computer from the Windows XP installation disc and install XP on the new-created partition. (Do not install at the wrong place or you may cover the WIN7 OS)
Step3. When the installation complete, now you will find you could only boot from Windows XP, the option Windows 7 is not at the boot menu.
Step4. Start your computer from Win 7 installation disc, select “Repair your Computer” at the main interface.
Step5. In next page, select “Command Prompt”.
In the pop-up window type the command below: one by one
bcdedit /create {ntldr} -d "Windows XP"
bcdedit /set {ntldr} device partition=D:
bcdedit /set {ntldr} path \ntldr
bcdedit /displayorder {ntldr} /addlast
After all of the command above works completely, now you could restart your computer and you may find a new entry for Windows 7 on your boot screen.