Well I am using this trick on my Ogero 512K. It's good, not too bad.
Ventrilo is sitting at 200ms all raid long.
WoW is around 350-480ms all day, except in raids it goes up to 540ms sometimes but it is playable and you can barely notice the difference.
I was using a program called PingFu from
www.artofping.com - it lowers my latency to 200ms :P but it is crappy in raids because of the burst in bandwidth when you engage a boss fight, you get some annoying disconnection with it sometimes.. so i'm better off without it