Quick question: to all of you who a) use or b) would consider using an anti-cheat anti-crash network filter, what would be a reasonable minimum system spec? Windows 95? 98? ME? NT 4? 2000? XP?

It will run under Windows 2000, as that's what my development machine runs. But I want to know if I need to support 9x, as it affects my choice of system APIs and just how I implement this (e.g. there's one way of writing this wich requires at least windows 2000, and another way which is not as good but will work under 9x/NT)