I had all kinds of problems trying to install XP to dual boot with Vista on my HP Pavillion dv6500t. I thought I would post my solutions in case anyone else is running into the same problems.
I successfully partitioned my drive:
D: HP Recovery
Then I tried to install XP, which returned an error message saying hard drive not found. After wandering through various forums, I found out that XP doesn't come with drivers for S-ATA drives. So I went to the manufacturer's website (Intel) and downloaded the drivers. The easy option would have been to install them from a floppy drive. But since this is a laptop, that really wasn't an option. The other option would be to disable S-ATA from the bios and install the drivers once XP is installed. However, HP locked down the BIOS and most of the features are unavailable. My only other option was to slipstream the drivers into the XP setup.
To do this, I used Nlite. While I was at it, I also slipstreamed SP2 and the drivers for my network card. But I hit another problem. Nlite only reads inf driver files but the Intel drivers came as an exe file. I tried the easy suggestion of extracting the files with Winrar but that didn't work. So I just installed the drivers on another computer (which was running XP, but I'm not sure that it matters). Then I searched for *.inf and found the Intel folder (C:\Program Files\Intel\...) where the setup dumped the drivers.
Once Nlite finished, I burned a bootable disc from the ISO with Alchohol 120%. Then I rebooted and installed XP.
I had all sorts of problems with VistaBootPro. I followed the steps in the How To guide but I couldn't get it to find XP. I eventually gave up and selected Add New OS Entry. I chose legacy version of Windows and named it XP. Then I rebooted. Now on my boot screen I had Vista, HP Recovery, and XP. But when I tried to boot into XP, I got an error saying the ntldr file was missing. It turned out that I needed to copy the ntldr (a hidden system file) that XP had dumped in my Vista root drive (C: which is my system drive) into the XP root (F:). Also, NtDetect.com needs to be with ntldr.
And I now have a laptop that dual boots into Vista and XP.