Sorry this reply is of no assistance only complaint of similar problem but on a Win7 64 bit version.
I had previously sucessfully installed ver 2011 and 2012 on the same machine.
When I started the program (2012) it notified me of upgraded version (2013) being available for download, to which I assented to the upgrade. Following the uninstall 2012 portion it choked when attempting the download of 2013 telling me I had no Internet connection, which was wrong on all counts.
It matters not how I attempt to install the 2013 version, from fresh boot up or not it balks with the same error message.
So here I sit with NO version installed for use and looking for a solution as well!
As typically happens, when checking a drawing for 30 mins, the errors become obvious the moment you push the print or send button...
I figured I'd download the package and install it directly since I was doing a stand alone.
Apparently I authorized installation of the Download Mgr on my computer.
I was unable to download the package at all. I finally deduced the Download Mgr may be the problem and disabled it from my MS Explorer 9. Download problem went away. So for whatever reason, Win 7 64 bit, Explorer 9, incompatability whatever. Downloaded the package (>700MB) and it installed successfully.
Things are working again.
Everyone with similar systems may wish to check for and disable Download Mgr to see if this helps...