it should have no effect on admission if the school offers group insurance (e.g. grad student) it should be ok. otherwise the worse is insurance not covering related medical expenses.
Windows at least until vista has horrible memory management. On my day job, at any given time every developer needs to run 3-4 Java VMs, each taking up 1-1.5GB memory, plus a browser and other typical office software. Those who do so on windows are constantly on disk swapping. I'm not exaggerating - if you hear the their hard drives spin, you'd think they are all hosting busy p2p nodes.