Glad you finally got it working! My Vista and XP change the drive letters around too. I think you can just set them to whatever you want in either operating system. Drive letters are set up by the OS and shouldn't affect the actual hard disc location. Vista stays as the C drive because it's the system drive. Then XP just dumps the rest in order after that since it can't read Vista's drive setup.
If you can't find the drivers on Sony's support site, try the manufacturer directly, such as Intel.
Thanks for the information about Dell! It seemed odd that HP was the only one doing it. I still have no idea why the ntldr keeps getting lost though.
The files need to go in your XP root drive, ie F:\ntldr, F:\ntdetect.com, F:\boot.ini
Mine are also in my Vista (system) root, C. (I'm not sure if that's necessary or not). Make sure you have a boot.ini file. If not, read skysurfer64's comment about using VistaBootPro to create a manual boot entry which points to the F: drive.