Office Home & Student 2007

I am trying to install this program on my 3rd computer. I am getting the

error code 1304: Error writing to file: Microsoft.Office.Interop.OneNote.dll

Verify you have access to that directory.

and another error code: 1712 This one had something to do with not being

able to go back to previous installed versions. I now need the product key

for 2003 to work.

My question is: How do I verify I have access (I am the administrator) and

where would I find the product key ( I don't have that disc anymore)

Thank-you