Have: Single partition firewire HD w/ 10.5.8 (my StartUp Disk), 2 bootable USB drives (1st= 10.6.7, 2nd= 10.8.2). Want: upgrade firewire HD to 10.8.2 Have:

a) single partition 2 TB external firewire HD w/ 10.5.8 (my current StartUp Disk)

b) single partition bootable USB drive with 10.6.7 (full version / not just an "upgrade" version)

c) single partition bootable USB drive with 10.8.2 (full version / not just an "upgrade" version)

Desired Outcome: run 10.8.2 on the single partition firewire HD (item "a" above)

Constraint: the single partition firewire external HD w/ 10.5.8 (current StartUp Disk) is a 2TB drive, and it also has other (non Mac OSX related) data files on the drive that I do not want to lose. To be clear, the constraint is that I do not want to erase this drive during the upgrade process.

System Details: 2008 Intel iMac 24", 4 gig RAM, USB 2.0, broken-ass internal DVD drive, broken-ass internal HD

My Question: how best to achieve the desired outcome? If not possible, please suggest next best alternative.

My Appreciation For Your Help: sincere &amp; immense :-)
You risk loosing your data in any upgrade.  You need to backup your important data. If your data isn't backed up, you do not have your data.

I recall you need to upgrade to 10.6 so you can do an online install of 10.8.  With an upgrade, the installation manager will not erase your data.  I have not tried this.

Robert