If you are taking this laptop back to work, then changing this could make it NOT work any longer. This appears because you need to log-on to a network domain, usually, but if your system admins say no problemo.
Easiest is to have Auto-Logon using Tweakui (from Microsoft, powertoys).
Alternately, if you want the standard WinXP logon screen, in the user control panel go to "Change the way users log on or off"->
Tick on "Use the welcome screen".
Either of these WILL create a security issue, since you don't actually need to know the password, or the alternate, you don't need to know the username to get into the laptop, or the entire domain, so don't be surprised if your IT department feels the need to haul your butt to the cleaners for changing this