I have multiple excel files. I want to have them all opened at the
same time in
different windows so I can alt-tab to each of them... Is there a way
of doing this?

These two different ways might help get separate windows for different
excel documents.

#1. From the Windows "Start" menu, use the cascaded menu to open Excel.
Once Excel is running, use "File Open" to open an Excel file. Repeat the
steps for the second file.

#2. Point to an Excel file on the desktop or in a folder. With the right
mouse button, click "Send To Excel". Repeat the steps for the second
file.

For #2, you might not see "Excel" in the "Send To" menu at first. To add it
there, put a shortcut to the Excel program into the folder
C:\Windows\SendTo\

By the way, if you have two files of the same name in different folders,
this allows you to have both open at the same time.

(I have Windows 98.)