i bought my BB off ebay and the previous owner had neglected to wipe it. they also forgot to tell me the password. i guess that is why it was so cheap
either way, just keep entering the wrong password, then typing blackberry, then enter the wrong password until the maximum number of retries is succeeded. at that time, the phone will do a self wipe - EVERYTHING but the OS will be wiped. user data, contacts, calendar items, pictures, ringtones, and everything NOT installed with the *default* os will be erased. I think the contents of your memory card will be safe.
it will be as if you had *just* gotten the phone from your carrier and just turned it on for the first time. the phones default themes, service books, WAP configurations...etc will be in place.
hope that helps.