well i've got a razer bs2k, and i have never regretted buying it(well took some time getting used to, and i was doubting it's potential a bit at first), but when you first get used to it you'll never switch back to another mouse.
but if you are thinking of using this mouse for office aplications then i'd say it would be a waste of money, me myself am an avid gamer, where the boomslang easily improves my rail in q3a.
i myself use win98se and no problems there.
2 of my clan members use it with win2k, and they don't have any problems either, so if your'ere going to use it for gaming buy it now.
also a smart move would be to get a great mousepad for it, i'd recomend the icemat www.icemat.com, a revelolutinary mousepad made of glass, else i'd opt for the func 1030 mousing surface