Arggg... Nasty Trojan! Any advise?

I have such a long story and will try to make it as short as possible.

My son has an HP laptop running XP. We have Norton on it and set the virus scan for around midnight. Of course... why would someone like me with a brain think that it would scan if the stupid thing wasn't turned on around midnight? Needless to say my son ventured a bit too far and to some slimey websites and got a virus.

I'm not positive the name but on occasion I get a Trojan 'looksky' popup.

This is what I did... and it took my all day to do it as the stupid popups were coming at me like crazy. I finally downloaded TrendMicro Internet Security (which made me delete all Norton) and it did an update and then a scan. It found well over 120 spywares and 3 trojans. All were fixed or quarantined.

Now after all of that I decided to take a break and shut the computer down and fix dinner. When I came back and tried to log onto IE, I get error messages. It seems that the trojan has changed his homepage to something like 'softwarereferral.com' and it will not load. I get error messages telling me that I can't load because something has changed. I then went to the control panel and tried to change his homepage to either AOL or default to microsoft.com but when I change it and click apply and exit...then go back it's right back to that stupid 'softwarereferral.com'

I've also tried to log onto AOL through their software and get an error that I have a firewall that is keeping me from logging on. (But I was logged on to AOL for the downloading of TrendMicro and had not problems.)

I hope this isn't too confusing and hopefully someone will come along to tell me what I need to do....hopefully something other than chunking the stupid laptop off a very high cliff!

Thanks in advance for any advise!