You will need to put your old SIM in, go to your O2 BIS website and click on support for your BlackBerry, find the place to setup BlackBerry Internet Service and put in the new PIN and IMEI number. If you have had BIS service to your old BB, that should be all that is required. Where can I log into my BIS account? - BlackBerryFAQ
I don't know why it is asking for a password. You said it was new, or was it purchased used? The previous user could have had a password on it and not removed it, or it could have been registered on a corporate BES system requiring a password.