You cannot save files in the Program Files directory without first running the program you're editing eqhost.txt with as an administrator in Vista or Windows 7. To edit this file, go to the start menu, type Notepad in the search box and then right click on Notepad when it appears. Select "run as administrator" and then open the eqhost.txt to edit and save it.
Alternatively, you can
temporarily disable User Accounts Control to edit/save the file without any of the above nuisance.