I successfully added Windows 7 Pro to my XP SP3 machine in a dual boot configuration when I purchased W7 upgrade a year ago. I followed the articles by Greg Shultz on ZD Net and it worked like a charm. Any Restart would take me to the dual boot window, I selected the partition to boot into and everything else followed smoothly. Although I rarely use XP any longer there remain one or two apps that require it. XP simulation in Windows 7 is not an option as my CPU does not support it. Nor does compatibility mode help as this application (an Okidata printer monitor, that is required for cartridge or drum changes and which they refuse to upgrade to a Windows 7 version) does not work in it.
Awhile ago my XP partition became corrupted and I had to reformat the partition (but not the drive) and reinstalled XP into it. I learned too late that this would not work because the boot block of the older XP system would not support dual booting. Then when I did a restart, the dual boot startup window no longer appeared and the CPU booted into XP; the Windows 7 partition was there, but not accessible.I subsequently booted from the Windows 7 repair CD and after 2 tries was able to repair the boot sequence so I could launch Windows 7. However the dual boot startup window still does not appear, so that now I can boot into Windows 7, but not into the XP partition.
Any help or suggestions, other than backing up the entire drive, repartitioning the entire drive, intalling XP into a blank drive, completing the XP installation, and then repeating the process of partitioning the drive, installing Windows 7, and then reinstalling all applications and data back into Windows 7, would be much appreciated.