Internet Explorer problem, please help....!

I have an Internet Explorer problem on a machine I built for a friend. When you open a web page I get a "IE has encountered an errror and must close", " do you want to send the info or dont send info", you know the message.
Well it doesnt matter if you click send or dont send, the page closes. Sometimes you can drag the error box to the bottom and continue using the page, but some sites dont work, they just close anyways. This is very annoying and Ive tried everything I can think of to fix it.
Finally i formatted the drive and reloaded. Everything worked fine for her for 5 weeks. Now its doing it again. She has up to date Norton and Pest Patrol Corporate, nothing out of the ordinary found there. The machine runs flawless other than this problem. She did download Google earth and of course it automatically downloaded the infamous "google toolbar", which I promply un-installed both. I dont know if that did something to IE or not but I did set IE back to default settings under internet properties. Im at witts end, can anyone offer ideas?

X2-3600
Msi M-atx w/onboard vid
1gb Kingston DDR2-667
CM extreme pwr 550w
XP pro

No I havent, I'll try that. Never used firefox.
Norton is for virus and the pest patrol is for pests/spam. Ive used both programs for a number of years thats why I insisted she have them on her computer. I also had those programs on the previous computer I built her.

Do you have the Yahoo toolbar installed? I've seen it crash IE.

Grumpy