Rooting Motorola Milestone/Android phone?

I am having problem rooting my milestone
When I use putting update.zip to sd card method
“E:Can’t open/cashe/recovery/command” error shows up
and when I use easy root, for some reason it says my phone is already rooted. but milestone overclocking and other rooted apps does not work and tell me I need to root my phone.
The phone wasn’t new when I bought it so I am not 100% sure whether previous owner rooted the phone….
What should I do??? Factory reset didn’t really help
any idea what I should do????