Using A Windows PC To Recover User Data From HFS Drive (dead Macbook)
If you're seeing 50GB worth of sparse bundle bands, this suggests that the user has implemented FileVault encryption on the volume. To the very best of my knowledge, it is not possible to mount sparse bundles from Windows systems. You'll need a Mac system of equivalent OS version or newer to mount the drive and the user will need to supply the password used to encrypt the data.

This should help with mounting sparse bundles externally:

http://support.apple.com/kb/TS1974