By default, Excel 2003 opens workbooks in the same window, which can make it difficult to compare and move portions of data between large worksheets. When you have multiple monitors, it makes this behavior even more annoying. Oddly enough, separate buttons on the taskbar are created, but the files are edited inside the same window. Fortunately. there’s a way to change this.

Here’s what you normally have to work with in Excel  to switch between files.

Excel Opens files by referring to the Open command options in Windows’ file associations.
Open Explorer and click Tools, then Folder Options.
Click the File Types tab and scroll down and highlight the XLS format.
Click the Advanced button
Select Open from the list of Actions and click the Edit button.
At the end of the box labeled “Application used to perform action”, add “%1″ including the quotes.
Uncheck the Use DDE checkbox.

Click OK on each window to get back to your desktop and double-click a few XLS files. They will open in separate windows.