Definitely avoid windows, its horrible not only because of security issues but also performance. FreeBSD is definitely the way to go and like someone said before if you cant justify a decent price for a dedicated server then you definitely dont need one. If you are looking for about 500GB of bandwidth to burn hit me up on icq at 36837470 I can set you up on a semi-dedicated machine (a couple of users per machine) with pricing very near $99 over quality multihomed bandwidth like Level3, MFN Abovenet, NYIIX, and others.
Good luck.
