I'm not absolutely certain but generally accounts have to be set up. I don't have SP2 in so it may be a 'feature' of SP2. Have a talk with the people who overhauled your computer.
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Open up the Microsoft Management Console (i.e. "Computer Management") under Administrative Tools in Control Panel and you will find a number of user accounts that are used for internal purposes. The ASPNET account is for running the "ASP.Net worker process" and you likely have it if you have installed IIS (Microsoft's web server) on your XP system. Generally only developers do this, but some application you have installed might conceivably do it. Have you installed any Microsoft centric Web development tools?
It's a little difficult to install IIS without knowing it, but if you want to see what is going on at your website, try putting http://localhost/ in your browser. That's the home page of the web site on your machine.
P.S.:
If you want to uninstall IIS (not a problem if you don't develop web sites for a hobby or a living), then follow the steps below:
1) Click on the "Start" button and then click "My Computer". This will bring up a new window.
2) Click on "Control Panel" under the "Other Places" section. This will again bring up a new window.
3) Double click on the "Add or Remove Programs" icon.
4) Click the icon on the left that says: "Add/Remove Windows Components".
5) Scroll down to "Internet Information Services (IIS)" and deselect the checkbox.
6) Click "Next". This will uninstall IIS from your computer.
Once this is all finished then you will be good to go and not have to worry about ASP.NET.