If you can recover the iPhone backup files that iTunes created from the hard drive (such as via an external enclosure like unepipe mentions), you should be able to recover the messages contained within. Messages are stored in a SQLite DB within the backup (this is how jwz's script reads them).
Looks like iTunes on XP stores backups at this path: \Documents and Settings\(username)\Application Data\Apple Computer\MobileSync\Backup\. That's the directory you need to recover from the hard drive.
Looks like iTunes on XP stores backups at this path: \Documents and Settings\(username)\Application Data\Apple Computer\MobileSync\Backup\. That's the directory you need to recover from the hard drive.