Grid computing needs and education

[Scott R. Ehrlich]

I know grid computing takes advantage of unused CPU cycles in other 
people's systems.

I have a network of heterogenious systems (Macs, Windows, Linux - Debian, 
CentOS, Fedora) I'd like to utilize grid software on.  What is the best 
way to approach this?  What grid software do people recommend?  How do I 
configure the subnetting (the systems traverse at least three subnets), 
and some are on a dhcp network with no corresponding hostnames - IPs 
only).

Thanks.

Scott