there are two answers to this question...
see attachments to this post.
attachment excel1.
if you right click the program icon on the taskbar and select the program again you can start a second copy of the program.
yes just clicking the icon and clicking it again causes it to maximise/minimise, but a right click, then click on the program name causes a second copy to be launched.
method 2:
see attachment excel2, you'll find a small minimize/shrink/maximise button just under the main window ones.
press this and the window shrinks.
you can now have as many workbooks open as you like all inside the same program and the same window (attachment excel3)