winzip/winrar etc are applications themselves, hence can be configured to run in compat mode. Whether this has an impact on how it works within KOTOR within Vista.... I dont know. Best way is to try and find out
yes, .net 3.x deploys on xp as well.
are the details directly from MS and here you can click to download full standalone package
questions here. The folks at workbench are infinitely more qualified to address code related queries.