Can't mount ddrescued Mac HDD - please help

Hello there. I am very new to the world of Ubuntu but learning as I go along, but apparently not enough to help a friend in need. Long story short: my friend's son with a MacBook Pro laptop was editing a video when his laptop just shutoff. Then came the clicking sound and the morbid realization that there's no backup - three years worth of undergraduate studies went up in smoke. I poured over the forums, built a simple Intel-based PC, installed an Ubuntu distribution and started learning how to recover his work. The imaged his corrupt 250GB HDD (assuming it's Ext3 Journaled fs) onto a brand new 500GB WD drive using Ubuntu Recovery Kit CD (used -f -n switches). Six hours later had an image done. But know I can't mount the drive. The GUI interface (I booted off of a dedicated SATA Ubuntu drive with that 500GB hooked up as a tandem drive). The GUI Ubuntu in Computer lists it as "500 GB drive: 250 GB File System", but it can't mount it with the following error message:
Error mounting: mount: wrong fs type, bad option, bad superblock on /dev/sda2,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
       dmesg | tail or so
I tried fdisk -l and this what I get:
root@owner-desktop:~# fdisk -l

WARNING: GPT (GUID Partition Table) detected on '/dev/sda'! The util fdisk doesn't support GPT. Use GNU Parted.

Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x00002161

   Device Boot Start End Blocks Id System
/dev/sda1 1 488397167 244198583+ ee GPT
Partition 1 does not start on physical sector boundary.

Disk /dev/sdb: 160.0 GB, 160041885696 bytes
255 heads, 63 sectors/track, 19457 cylinders, total 312581808 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00053bdb

   Device Boot Start End Blocks Id System
/dev/sdb1 * 2048 310523903 155260928 83 Linux
/dev/sdb2 310525950 312580095 1027073 5 Extended
/dev/sdb5 310525952 312580095 1027072 82 Linux swap / Solaris
root@owner-desktop:~#
-----------------------------------------------
what in the world is '/dev/sda'! and what do I do know? Notice that the PC is running off of dev/sdb and that the 500GB drive became an sda drive.
I can feel the data is there but how do I get to it. Arghhh. I need your help folks - the last thing I want is give this kid bad news and his family is not in a position to shell out $$$$ for data recovery. Any help is greatly appreciated. I know very little when it comes to Ubuntu so if you could please spell all the commands out, i.e. here's step 1, step 2, etc. Thank you! Arthur