This is what I found, I have never tested it so use it at your own risk.
Maintenance and Service
Guide
HP Pavilion dv4000 Notebook PC
Compaq Presario V4000 Notebook PC
Resetting the Computer
If the computer you are servicing has an unknown password,
follow these steps to set a new password. These steps also
clear CMOS:
1. Enter an incorrect password and press enter.
2. Repeat step 1 two more times.
After the third entry of the incorrect password, the computer
responds with a “System Disabled” message and provides an
override password.
3. On another computer running Windows XP, download the
unlock6.exe utility from the HP Channel Services Network
(CSN) Web site. Copy the
unlock6.exe utility into the root directory (C:\ drive).
4. Access MS-DOS by clicking Start > All Programs >
Accessories > Command Prompt.
5. Enter unlock6 xxxxx 0, where “xxxxx” is the password
generated by the computer in step 2.
The computer responds with another system-generated
password.
6. Enter the password generated in step 5 on the disabled
computer to enter the system BIOS. In the BIOS, navigate
to the Security tab and Administrator Password. Enter the
password generated in step 5 as the current password. Enter
a new password to change it.
7. The password has been reset and all CMOS settings have been retored.
Unlock6 Download.