Clean wipe iMac running 10.4.11 OS X? We recently bought a used iMac, (iMac7,1 running Mac OS X 10.4.11 Build 8S2167), from a garage sale. 

When I plugged it in I saw that the previous owner didn't factory reset it. 

He left his admin account registered with password, so I can't just erase his account and make a new admin account. Apart from this it limits me to some programs I'd like to install.

I don't have the installation disc I need (as read looking around through other forums).

And Command R is not working for me on startup. (or Control  R  since I'm using a Windows keyboard).

I've read that I can download a digital version of the installation program.

Can I start it up from a USB? as i do not have "FireWire" or another Mac. 

If so can I have a link to the right torrent I'm looking for?

What are the steps I need to make this work...?

I have little to no knowledge about Macs, this is my first Mac.
Emerald, amigo:

Let's get your Mac working for you:


Reboot the machine, holding down the appropriate keys on your
 windows keyboard to effectuate an Apple COMMAND-s.  Two keys here, 
 the 's' for single-user, and whatever key maps to the COMMAND, or 
 APPLE key.  If all goes well, then a nerd-screen, like a DOS prompt 
 or UNIX shell will appear instead of the normal boot process.  
Please execute the fsck as it is suggested above your command prompt.
Should be something like 

      /sbin/fsck -fy

Let's mount the root partition in read write mode:

      /sbin/mount -uw /  

Carefully delete the one file in the way of your enjoyment of your
new Mac -- no re-installation shenanigans required:

     rm -f /var/db/.AppleSetupDone

Proper restart:

     sync ; shutdown -r now



Next, create your new admin account, as if this was the first time you ever used your new Mac.  

Enjoy,

F.