Hi, no eMacs had G3s, only G4s. Is it maybe an iMac G3?
If you don't know the model, find the Serial# & use it on one of these sites, but don't post the Serial# here...
How to find the serial number of your Apple hardware product...
This is not a new idea as it has been done many times. Supposing this is an eMac, you can disassemble it and remove the hard drive if you wish. It all depends on whether you feel capable to do this. If your computer won't start and the hard drive is a concern, there is no other path but for you or someone else to do this. If some guy in an Apple store has freaked you out, then get someone who is capable and confident with electrical equipment to dismantle it for you.