Nope, you cannot repair it from a Windows computer.
For Snow Leopard, there is no recovery partition. That was introduced with Lion.
So, at this point, your options are:
1) Get your hands on a Mac OS install disc either from a friend or buy one.
2) Hook the Power Mac G4 up to another Mac by way for the Firewire port and boot into Firewire Target mode. This will cause the Power Mac G4 to act like an external Firewire drive for the other Mac. From there, you could try repairing the drive using Disk Utility or some third party utility such as DiskWarrior or TechTools Pro.
3) Try booting from a third party utilities (such as DiskWarrior or TechTool Pro) bootable optical disc. If you don't have either utility, you will want to verify that the optical disc that they ship you is in fact bootable (I don't own DiskWarrior and it is has been a while since used my Tech Tool Pro disc so I don't recall if it is bootable).
4) I suppose you might be able to take it to an Apple Store. You might have to pay to have them boot from an installer disc and either reinstall the OS or repair the OS...but they might let you borrow the disc while you sit there.
5) You could see if you could find a local computer shop/tech who deals with Macs. This undoubtedly will require you to pay.
I honestly don't know if you can still get a Snow Leopard disc from the Apple Store or not. You would need to try calling the Apple Store 800 number (800-MY-APPLE) as I seriously doubt they will have it available for purchase in a local Apple Store. If you cannot, then your only option would be to buy it used through a site like eBay.
Edit: Removed the option about removing the hard drive. I forgot/got confused as to which model it was...forgot it was an iMac when you called it a PowerMac G4. If it is an iMac running a PowerPC processor, then it will be a major effort to remove the hard drive. If it is an actual PowerMac G4 tower (i.e. NOT an iMac), then removing the hard drive is very easy.
Edited by smax013, 30 March 2013 - 11:14 AM.