As I said, there is no general recipe to go into the BIOS and change the boot priority. You'll have to find out yourself or post more details about make and model of the PC and what BIOS it has. But since it doesn't harm at all to have the optical drive (CD, DVD) first and the hard disk second, it's totally unimportant to change it back.
External hard drives can be used without any additional driver. Those are built into Windows already.
The URL to download Internet Explorer 8 has been given above already by wpgwpg, as
After installing that, all your issues should be solved, I think. If not, tell what still is wrong.