It won't matter if you wait for Leopard or not (btw, rumors are that it'll be released by the time you're ready to buy), so that point is moot. Even if it isn't out, it'll be a $100-$150 upgrade.
There is a little program called boot camp that will allow you to choose which OS you want (this includes Linux, too, btw). More rumors have it that dual booting be part of Leopard, instead of an add on program. (It'll probably be able to boot Vista, too.) The good thing is that a lot of the programs that you already have will run on the new machine with boot camp.
About the only thing that you will need in order to network is a ethernet card, if you don't have a wireless network, as all the Macs have wireless cards built into the machine.
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There is a little program called boot camp that will allow you to choose which OS you want (this includes Linux, too, btw). More rumors have it that dual booting be part of Leopard, instead of an add on program. (It'll probably be able to boot Vista, too.) The good thing is that a lot of the programs that you already have will run on the new machine with boot camp.
About the only thing that you will need in order to network is a ethernet card, if you don't have a wireless network, as all the Macs have wireless cards built into the machine.