I know the following works for 2003 and 2000, you are welcome to try it
on 2007.
Since the problem is ONLY when you double-click on a file to open it.
the problem may be due to DDE. It can be fixed by reinstalling Office,
OR this workaround.
Go to Control Panel, Folder Options, File Types, scroll down to and
select XLS (for Excel files)(or DOC for Word files), click Advanced,
select Open entry, click the edit Button.
Now uncheck "Use DDE" and then put your cursor in the Application box,
arrow all the way to the right and put in "%1" (include the quote
marks), IF there is /dde remove it. Then OK your way out, things should
work quickly again.