Your first priority should be to enable XP's firewall:
http://www.microsoft.com/security/protect/

A security issue has been identified that could allow an attacker to
remotely compromise a computer running Microsoft Windows and
gain complete control over it. You can help protect your computer
by installing this update from Microsoft.
http://www.microsoft.com/downloads/details.aspx?FamilyId=2354406C-C5B6-44AC-9532
-3DE40F69C074&displaylang=en

Afterward, visit the official Windows Update website and
scan your new computer for new updates and install them.
http://v4.windowsupdate.microsoft.com/en/default.asp

Greetings --

   The salesman was partially correct. (Which puts him head and
shoulders above most Best Buy sales personnel.)  You are most
definitely at risk if you access the Internet with an unprotected
computer.  But, the first thing you should do is enable WinXP's
firewall, otherwise you'd be likely to in infected with Blaster while
trying to download the necessary patch.  ;-}

Protect Your PC
http://www.microsoft.com/security/protect/default.asp

      If you were to connect the PC to the Internet without having
first installed the KB824146 Hotfix, without having first installed an
antivirus application with current virus definition files,  or before
enabling a firewall, you're very likely to get infected from any of
the thousands of PCs on the Internet that are constantly broadcasting
the Blaster and/or Welchia worms.  It only takes a few seconds of
exposure.

Microsoft Security Bulletin MS03-39
http://support.microsoft.com/?kbid=824146

What You Should Know About the Blaster Worm
http://www.microsoft.com/security/incident/blast.asp

W32.Blaster.Worm  a.k.a. W32/Lovesan.Worm
http://www.symantec.com/avcenter/venc/data/w32.blaster.worm.html

W32.Welchia.Worm a.k.a. W32/Nachi.Worm
http://securityresponse.symantec.com/avcenter/venc/data/w32.welchia.worm.html

Bruce Chambers

--
Help us help you:
http://dts-l.org/goodpost.htm
http://www.catb.org/~esr/faqs/smart-questions.html

You can have peace.  Or you can have freedom.  Don't ever count on
having both at once. -- RAH