All of the above fixes work but only once. they must be repeated each time. If you want it to be permanent you must change the file association. This is a list of the default programs to launch for each file extension.
To change this permantly there are instructions in the Windows help file. Below are the instruction for changing the association in win 98 quoted from the Help Menu.
To change which program starts when you open a file
In My Computer or Windows Explorer, on the View menu, click Folder Options.
Click the File Types tab.
In the list of file types, click the one you want to change.
Click Edit.
In Actions, click Open.
Click Edit.
In Application used to perform action, enter the program you want to use to open files that have this extension, and then click OK.
Note
The settings for selected file types are shown in File type details.