Can you slave to 80GB drive and boot witht he old 40GB. Then maybe once you are in XP you can go to manage and use disk utliities there to pull up information or use partion magic to read the drive.
Just a guess without seeing the system, but before completely wiping the drive I would do that.
U can not change or install MBP and can not create pertition.
1. First you go to connect separate new cable for 2 HDD. Then you boot a hard disk where win-xp install. If the cable problem then solve.
2. If not solve then u install data recovery tools (i.e. paretologic data recovery, ontrack data recovery) and search that unknown partition and recover files.
3. If not solve then u install that hard disk to other computer if possible.
Three of them no.1 is very important.
There might be an error to your hard disk drive sectors. Basically, this error occurs when the particular sector is damaged and cannot store the files properly. Instead of displaying some errors, it just suddenly stopped.