The main difference between Mac OS X 10.5 (Leopard) and Mac OS X 10.6 (Snow Leopard) is that Leopard is the last version that will run on the older Power G4 and G5 processors. Snow Leopard and subsequent versions (such as Lion) will only run on Macs with an Intel processor.
Consequently much of the differences between Leopard and Snow Leopard were in the inner workings of the system which were rewritten to take advantage of the Intel processors and to strip out the old PPC code resulting in a faster and smaller system.
Although the appearance of Mac OS X 10.5 (Leopard) and Mac OS X 10.6 (Snow Leopard) is similar there are many differences in the workings of the two systems. Most notably Snow Leopard requires a Mac with an Intel processor whereas Leopard will run on earlier Macs with G4 or G5 Power PC processor as well as the newer Intel based Macs.
10.5, Snow Leopard is 10.6
It is probably going to come out after OS Snow Leopard
Mac OS X 10.6 (Snow Leopard) and all earlier versions of Mac OS X will support networks.
yes
Snow Leopard needs to be purchased on a disc it can then be installed to update Mac OS X 10.5.8
Snow Leopard runs optimally on 2GB of RAM.
All new Macs have Mac OS X 10.6 (Snow Leopard) installed.
Mac OS X 10.6 (Snow Leopard) is only legally available to buy from a software retailer.
Although technically an upgrade to Leopard (Mac OS X 10.5) the Snow Leopard (10.6) disc does have a full installer and so can install the software onto a blank formatted disc with no existing OS.
All new Macs are supplied with the latest version of Mac OS X which is currently 10.6 Snow Leopard.
To upgrade from Mac OS X 10.5 (Leopard) you need to buy a copy of Mac OS X 10.6 (Snow Leopard). Snow Leopard only works with Macs with an Intel processor; Macs with PPC processors (G4 or G5) can only go up to Leopard.