<iframe width='500' height='500' frameborder='0' src='https://spreadsheets.google.com/ccc?key=0ApILEVmEy4YHdGRTdGZNTWd1cmc2c0RPN0dtSnZGWHc&hl=en'>
This Code dispays spreadsheet in some bowsers.In all bowsers it shows spreadsheets but ie it shows login page
I tried too many things at once, so I missed what actually fixed it. Accepting 3rd party cookies worked.
It could be security settings since that link is encrypted via https and (perhaps) your parent page is not. IE usually throws warnings when you use secure/insecure items in the same page.