I'm going to look at it from an even more basic perspective. What do your classes require?
I'm willing to bet they don't specify a certain OS. None of the network classes I took ever required me to have a specific OS at home.
It's going to depend on how the school's curriculum is set up, but I suspect most of the classes are going to be testing knowledge of network standards, physical mediums, the OSI model (which will be drilled into you), how traffic gets routed, how packets are encapsulated, etc, etc.
By the time you get to actually doing labs, it will likely be for routing and remote access, in which case all you'll need is a telnet/ssh app like PuTTY.
If you want both OS's to expand you're knowledge, then by all means go for it, but I doubt your classes will really have a requirement for one or the other. And if they do, the school has to provide computer labs with the necessary equipment anyway.
I know there are a few network engineer's (which I am not) on here who could probably give a bit more guidance on what you'd really want to have if you wanted your own test lab.
Just food for thought....Don't want you spending money you don't need to
