If you are running Windows ME or XP you can use the System Restore function to go back to a time prior to installing the IE 6 upgrade. This will restore your system to the state it was in prior to this installation, unfortunately it will also render useless any programmes you have installed since, although these can be installed again.
If you are running Windows 98, go to Add Remove Programmes in the Control Panel and remove IE 6. This should restore your previous version, although if it dosn't you can reload it by re-installing windows.
If you are running a Mac ... You're on your own, and good luck.
Alan, Canada