Have just got a new 7920
Without a sim, it is displaying new password, but dont know if i have to create
a new password ,or if i put my own sim in would my pin number work,any advice how to get started would be appreciated.

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.

Sorry did not explain i bought it used, why is everyone disgruntled, i am new to the blackberry so am completley in the dark..

No one is disgruntled. No postal workers around. You asked questions and were given answers.

No disgruntled people here! Like JSanders said, there very well could be a password on the device from the previous user. Have you tried to enter in a password? If so it should either say incorrect password or verify password. I am thinking that the device was on a BES and the previous user did a wipe on the device and it is asking for a new password due to the IT policy on the device.

Nelski, all very gruntled here. Read my signature! Happy Happy Happy.

Your post said it was new, and from your description, I guessed it was used, so I wanted to clarify. Do as described here to clear the IT Policy, and you should be good to go.
Remove IT Policy - BlackBerryFAQ

AND--welcome to the VERY un-disgruntled Forums. Very.

Nice Sig! I love the office and Dwight Shrute it the MAN!

Type the wrong password in 10 times and the device will erase all the previous user's data and allow you to enter a new password.

Then follow the instructions on removing the IT policy.

All "gruntled" here!!