Well, the few times I played around with Kazaa I noticed that it gave me all kinds of trouble when I tried to have Internet Explorer and Kazaa open at the same time. Basically, Internet Explorer would never work if Kazaa was up and running. So if I were you (or her), I would try to uninstall Kazaa then try to reinstall IE6. If that doesn't work, then you should try a complete virusscan of the system (not a bad idea anyway as long as your .DAT files are up-to-date), maybe a adware cleaner such as Ad-Aware, and also maybe a registry cleaner. Basically, a general cleanup of the system.

BTW, where is she trying to install IE6 from? Microsoft's website, or from a CD somewhere?

Just a side note, if she insists on running Kazaa she'll need to stay up-to-date with her virus .DAT files and make sure that she has a good HW or SW firewall running.