Here is my problem.
When I double-click an Excel file in Windows Explorer the file opens in
Excel 10 (XP), which is what I want. However, when I open subsequent Excel
files using the same technique, a new instance of Excel 10 is open, rather
than simply opening in the already open Excel instance.

What I think caused it.
I recently loaded Office Basic 2007, but I disabled Word and Excel, and am
only using Outlook 2007. But I guess I still managed to mess up the registry
for Excel, which is my only guess as to what is causing the strange behaviour
in Windows Explorer.

What I have done to try and fix it.
I searched the disscusion groups and found a great post by Dave Peterson
about re-registering Excel. So I did that. StartRun"C:\Program
Files\Microsoft Office\Office10\excel.exe" /regserver. Looking in the File
types under folder options in Window Explorer it seems to have re-associated
Excel file types with Excel 10, at least the icons changed, but I still have
this problem of multiple instances of Excel (same version 10) being opened.

--
Casey