Clean wipe iMac running 10.4.11 OS X?
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.