Identifying which Mac OS X

Is there a way to identify which version of Mac OS X a Mac is running by viewing the files on the hard drive (i.e. not booting from the volume, but looking at it externally through Target Disk Mode)?

Pretty much the situation is I have a Mac is suffering a Kernel Panic, but I only want to install the version of Mac OS X that they have (i.e. I'm not going to give them a free upgrade). I do know that it has to be running at least Tiger (Its a Santa Rosa MacBook Pro).

Are there any identifying files on the Hard Drive that can be unique to each 10.4, 10.5 and 10.6 that I would be able to tell which version of OS X is installed?

Thanks in Advance.

A record of updates and installers can be found in

/Library/Receipts/boms/

That should tell you what the last update was

Not quite what I was looking for, but I found a different solution.

It's as simple as Wallpapers found in Library/Desktop Images.

If it doesn't have the "Aura" Wallpaper, it's Tiger
If it doesn't have the "Snow Leopard" wallpaper, it's Leopard
If it has both, it's Snow Leopard.

Thanks for your input anyways!