Opening Seperate Excel Instances with Windows 7

Since having upgraded to Windows 7, I can no longer open a new/seperate Excel instance to compare files, without having to open a new instance from the Excel Icon on my desktop and then opening a saved file using the "Open" feature within Excel.

For Example; I have two Excel attachments from an email that I would like to open in seperate Excel instances to compare data. If I have 2 seperate Excel instances open (using the Excel icon from my desktop both times), and try to open one of the two files it would open in the first instance Opened. Then if I click on the 2nd instance I opened earlier to make it active and try to open the 2nd file it will open in the first instance rather than the 2nd one I last made active.

So currently as my work around I have to doucle click or right click to open one Excel file which would open a brand new Excel instance (given that there are none already open). Then to open the 2nd Excel file I would have to save a copy on my computer > open a new instance using the Excel icon on my desktop > and go file Open to open the file.

Question: Is there any way I can have it where a new file will always open in a new instance?

This is for work and I have dual monitors and need to compare large amounts of data at a time.

When I use two monitors I do this
open first excel file and move to other monitor
then go to programs and open excel then other file

Great, thanks