How to open Excel files in separate windows in Windows7
Ughh, this drives me crazy and there are several other sites showing the regedit but I felt most comfortable running Microsoft FixIt and letting it do the work.
http://support.microsoft.com/kb/2636670
Article ID: 2636670 - View products that this article applies to.
By default, Excel files are opened in a same window in Windows 7. But sometimes you might want to view some files at the same time on your screen. To do this, you can start a new Excel process (excel.exe) by clicking the Excel button from the Start menu.
However, you can configure your computer to always open Excel files in separate windows. We recommend that you only use the method in this article when your computer has sufficient RAM.