Well, the hex leaves me cold, but I think it's safe to assume that the UNMOUNTABLE_BOOT_VOLUME message indicates that the computer's unable to mount the boot volume of your hard drive.
I've experienced similar errors myself, and it's usually because I did something to corrupt the boot sector of my hard drive. If you didn't do anything special before this error manifested, my best guess would be that a virus or something messed up your parition table.
If you have the XP installation disk, you could try booting up with it and entering "console" mode. There, you can try entering the commands FIXMBR or FIXBOOT, which should rewrite your master boot record and your boot sector, respectively.
That's my advice - keep in mind that messing around with partitions and boot records can permanently trash your data, but at this point you haven't got much to lose, have you?