Admin Password in Win XP Repair...

In your case you have indicated that you get the stop error "IRQL_NOT_LESS_OR_EQUAL".

This indicates that you are using a driver that is incompatible with Windows XP.

Most likely as you suggest this is for your BT ADSL modem.

First contact the manufacturer for Windows XP digitally signed drivers for this device and check all other as follows:-

This step-by-step article describes how you can use the Windows XP Signature
Verification tool (Sigverif.exe) to find unsigned drivers and verify device
drivers in Windows XP. This information can be helpful for troubleshooting
system instability, error messages, boot problems, and so on.

Verify Unsigned Device Drivers
------------------------------

1. Click Start, click Run, type "sigverif" (without the quotation marks), and
then click OK.

2. Click Advanced.

3. Click Look for other files that are not digitally signed.

4. In the Look in this folder box, type "x:\Windows\system32\drivers" (without
the quotation marks), where x is the letter of the drive where Windows XP is
installed.

5. On the Logging tab, make sure the Save the file signature verification
results to a log file check box is selected, and then click OK.

6. Click Start.

NOTE: The log file is named Sigverif.txt, and it is saved in the Windows
folder. Third-party drivers that are unsigned are displayed as "Not signed."
Use the drivers in this list as your troubleshooting starting point.

Disable Unsigned Device Drivers
-------------------------------

A common problem is power management features, and Microsoft requires power
management support to certify drivers. Many third-party unsigned drivers lack
this support, resulting in power management problems (such as problems going
into or coming out of hibernation and standby).

After you find unsigned drivers, you can disable them by using any of the
following methods:

- Disable the device in Device Manager (you may have to click Show hidden
devices on the View menu, and then disable the device under the Non-Plug and
Play Drivers branch).

- Uninstall the software that installed the third-party driver by using the
Add/Remove Programs tool in Control Panel.

- Rename the driver in the Winnt\System32\Drivers folder.

Troubleshooting
---------------

If you have multiple unsigned drivers, disable them one at a time. If disabling a
driver resolves the problem, contact the manufacturer of the third-party system
driver for a updated version that is designed to run with Windows XP.

Hopefully this will be of help.