Compatible? -Powermac w/Leopard Server and iMac w/Lion

My main computer is 2009 iMac running regular Lion OSX 10.7.4. I have an old Single Processor 1.8 Powermac (7,2). I want to use the Powermac as a server, running Leopard 10.5.8.

1. Will this work in terms of the two different operating systems coexisting?

2. Do I need to downgrade my iMac to Leopard to match them up?

3. Can I install Lion Server on my iMac to make it a controller, and use the Powermac as a server and assist with rendering projects? (I do professional video and photo editing)