Will a imac G4 700Mhz run OSX leopard 10.5 ?

Officially, it can run no higher than OS 10.4.11. The installer for OS 10.5 looks for an 867mHz or faster to proceed.

There are third-party hacks that let you trick the installer to allow installation on unsupported G4 Macs. Howwever, consdiering that I find 10.5 sluggish relative to 10.4 on a much faster G4 1.25Ghz minitower with a lot of RAM and better video hardware, I'm not sure it's worth it.

Even if you manage to install 10.5, you are stuck with USB 1.1 ports that won't fully support the current generations of Apple iDevices.

If you really want a desk lamp iMsc for the design (which is very cool) yet intend to use the computer for something other than a jukebox, walk away from the 700mHz model and spend the time looking for the last of that model. Those had a 1.25ghz processor, hold twice as much RAM, and have USB 2.0.