Raz
Here are the canned instructions for doing that.
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Delete user accounts first then.....
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REMOVE WINDOWS LOGON BOX
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Step 1- Click Start\Settings\Control Panel, and then double-click Network .
Step 2- On the Configuration tab, click Windows Logon in the Primary Network Logon box, then click OK .
Step 3- Do not Restart Computer if prompted! Click NO.
Step 4- While still in control panel click Passwords
Step 5- On the Change Passwords tab, click Change Windows Password , select any check box, then click OK
NOTE : If you cancel the network logon dialog box when you start your computer, the Change Passwords tab may not be available. You must log on so that the Change Passwords tab is available.
Step 6-In the Change Windows Password dialog box, type your current Windows password in the Old Password box. Leave the New Password and Confirm New Password boxes blank, click OK , and then click OK
Step 6- Exit Control Panel
Step 7- Click Start\Search-Find, then click For Files or Folders
Step 8- Type in *.pwl in the Named box, click Local Hard Drives in the Look in box, then hit ENTER
Step 9- Right-click one of the .pwl files, click Rename , rename the file with an .old file extension. Repeat for each .pwl file.
Step 10- Shut down and then restart your computer.
Reference material
remove user profiles
http://support.microsoft.com/default.aspx?scid=kb;EN-US;q156826
remove logon
http://support.microsoft.com/default.aspx?scid=kb;EN-US;q152104
Dave