I have a laptop that has the AntiVirus 2008/2009 fake alert and can't get rid of it.  Please help!

I have a Windows XP Laptop that has all the critical updates for MS, Symantec Endpoint 11 with the latest pattern file, but laptop still got infected with the AntiVirus 2008/2009 fake alert.  I have googled many sites to try and find a difinitive way to remove but most of them want you to purchase the program. That would be okay if I could be sure that the program would actually remove this nuisance trojan and at the same time would not install their own spyware on the system.  

I have tried to remove manually according to some sites I found, as well as installing the free version of SuperAntiSpware, and Spybot.  Both of these programs found some items and cleaned or removed them and after running a second scan showed that there were no problems.  However as soon as I accessed my browser the prompt appeared again.

Has anyone out there encountered this problem and if so what worked for you next to re-building the laptop in this case.  Any help would be appreciated.Start Free Trial

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The exact message that pops up is shown below complete with misspellings:
 
Windows Internet Explorer
Attention! If your computer is infected, you could suffer data loss, erratic PC behaviour, PC freezes and creahes.
 
Detect and remove viruses before they damage your computer!
AntiVirus 2009 will perform a quick and 100% FREE scan of your computer for Viruses, Spyware and Adware.
 
Do you want to install Antivirus 2009 to scan your computer for malware now? (Recommended)
 
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