Today I want to share some tips about the process of upgrading a PC to a dual-boot system, namely with Windows XP and Windows 7. What I needed was to have another partition containing XP SP3, because some programs were fully compatible only with that operating system.
First of all, I wanted to keep the 100MB partition which is created and installed by Windows 7. Several guides on the internet suggest to remove that partition, but I preferred to keep it. Remember that in a single OS PC, the 100MB partition has the boot flag, so it is used during the system boot.
Using the GParted iso, prepare the disk by shrinking the Win7 partition. Create a primary NTFS partition after thw Win7 one, which will be used for WinXP. After it, create an extended partition, and inside it, create a logical partition named DATA, which will be used to share data between the two OSes. This is done because it is preferred to hide each OS partition from the other, so the OSes won't interfere with each other.
Boot from the WinXP installation disc, install on the newly created XP partition. If you have any problem during the installation, like a BSOD (BLue Screen of Death), this is because the XP installation cannot control the SATA hard drive, because one of the BIOS options is set to AHCI. If this is your problem, enter into the BIOS, and change the storage parameters from AHCI to IDE. This will solve the XP installation problem.
After the installation, install the drivers of all the components of your PC, then go to administrative tools --> computer management --> disk management and remove the drive letters from the 100MB partition and the Windows 7 partition THis will avoid any interference by the XP system to the Win7.
At the next startup, change back to AHCI drivers, and wait for Win7 to start up. Install EasyBCD, which is a MBR (Master Boot loader) modification tool, and use it to add a new entry to the choice selection during the system startup. After finishing, push the button "Write to MBR" to save the edits.
After this, we must tell Win7 to change the hard drive control drivers, so they will be compatible with XP.
Do as stated in this useful guide:
Change SATA hard disk mode from AHCI to IDE after installing XP in a dual-boot system
At the next restart, set the storage parameter to IDE in the BIOS; Win7 will then load the IDE drivers, the same used by WinXP, so there will be no need tho change anything from the BIOS ever again.
Now the PC should start with the request to choose between XP and Win7. Boot into Win7, go to the "disk management" control, and remove the drive letter from the XP partition, so it will be hidden from the system, and no program will be able to modify its content.
Now you have a nice dual-boot system!!
If you have any problem, I suggest to keep a local copy of the Gparted live iso, and Hiren's boot CD, which is a powerful first-aid collection, full of useful programs for any issue.