I am a NOOOB

Welcome. Microsoft has a page on doing this:
http://support.microsoft.com/kb/295017

If you get lost, go to start, control panel, system and go to the Computer Name tab. At the bottom is a Change button next to the text "To rename this computer or join a domain, click Change".

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Ok, now the tough part, this changes the computer description only. If you are logging on under a name you do not like, which I think is what you want to do, there are a few steps to change that registered name:

Begin by first clicking on the Start Button.

Then click on the Run Icon, which will open up the Run Menu for you.

Type the word Regedit into the white area and then click on the OK button.

Click on the plus sign [+] next to HKEY_LOCAL_MACHINE to expand that section.

Then click on the plus sign [+] next to Software to expand that section.

Then click on the plus sign [+] next to Microsoft to expand that section.

Then click on the plus sign [+] next to Windows NT to expand that section.

Then click on the yellow folder entitled Current Version. Do not click on its plus sign [+].

Now move over to the right side of the screen and scroll down until you see Registered Owner.

Double click directly onto the words Registered Owner until it opens up for you.

There will be a white entry area entitled Value data: awaiting your input.

Simply type your first and last name into the white area and click on the OK button.

If you also want to add or change the Company information, then please continue onward.

Double click directly onto the words Registered Organization until it opens up for you.

There will also be a white entry area entitled Value data: awaiting your input.

Simply type your Company information into the white area and click on the OK button.

Now close the Registry by clicking on the X box located at the top right corner of the screen.

You must reboot your computer for the changes to take effect for Windows XP.