Currently, it's $129 dollars (Mac OS X Leopard). Once Snow Leopard is available (August 28), it will be a $30 dollar upgrade from Mac OS X Leopard.
Mac OS X 10.6 (Snow Leopard) and all earlier versions of Mac OS X will support networks.
Mac OS X 10.5 is known as Leopard. The last available version of Leopard was 10.5.8.
To upgrade from Mac OS X 10.4 (Tiger) to 10.5 (Leopard) you will need to buy a boxed version of Mac OS X 10.5. If you have a Mac with an Intel processor you can go straight to Mac OS X 10.6 (Snow Leopard) which is a cheaper upgrade option.
You need to purchase each version (Panther/Tiger/Leopard) of Mac OS X.Mac OS X 10.3 (Panther) can be updated to 10.3.9.Mac OS X 10.4 (Tiger) can be updated to 10.4.11Mac OS X 10.5 (Leopard) can be updated to 10.5.8
Apple's Mac OS X. OS X Lion OS X Panther OS X Leopard etc.
Mac OS X 10.5 (Leopard)
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.
Mac OS X 10.4 (Tiger) can be updated to Mac OS X 10.4.11 for free. Purchased upgrades then are Mac OS X 10.5 (Leopard) or Mac OS X 10.6 (Snow Leopard). Snow Leopard only works on Macs with an Intel processor. Older Macs with a G4 or G5 processor can only go up to Leopard.
Snow Leopard needs to be purchased on a disc it can then be installed to update Mac OS X 10.5.8
Yes, Mac OS X 10.5 Leopard ships with Java support.
Mac OS X 10.4 was called Tiger and Mac OS X 10.5 was called Leopard. The 10.5 (Leopard) version is better than the 10.4 (Tiger) version. They would not have sold many copies of Leopard if it was worse than Tiger.