You really didn't ruin anything.
You need to now find, purchase and install a retail version of OS X.
I would replace the PRAM battery and, also, install more RAM.
Your eMacs can take a total of 1 GB of RAM.
OS X needs all the RAM it can get to run smoothly, so just install the max.
I am kinda of in a bind to tell you which version of OS X to find, purchase and install.
OS X 10.5 Leopard can still be found rather expensively and you try calling Apple atn1-800-MYAPPLE and ask for software sales. Tell them you have an older Mac and just bought an iPad.
They might be able to supply you with a copy of OS X 10.5 Leopard.
The reason I hesitate to recommend OS X 10.5 Leopard is that your eMac has barely over the min. CPU spec. and barely enough RAM to run OS X Leopard.
I would rather see these eMacs stay on OS X 10.4 Tiger, but finding these retail discs now are not impossible to find, just even more expensive to purchase than OS X 10.5 Leopard.
My advice, if you know any Mac users that can loan you a copy of OS X Tiger to install, I would go this route.
Use OS X Disk Utility to reformat the drive as an HFS+ Extended format ( journaled), choose a partition scheme, then begin installing OS X.
Once installed and you have any apps installed in the internal HD, buy an external FireWire drive and use it to clone your internal to the external drive using an app called CarbonCopyCloner or SuperDuper. So, if you have any issues with OS X on your internal drive, you'll have a bootable and backup copy of the OS on an external drive for the future.
Good Luck getting these eMacs back up to running condition.
Forgot to mention that reliable RAM can be found from online resellers crucial memory or OWC.
Here are the specs for your eMacs RAM.
Memory Slots 2 - PC-133 3.3 volt, unbuffered, 8-byte, non-parity 168-pin SDRAM