That's about the hard drive space. There are two things involved here:

1. The program files that the install puts on your system. Most install programs have an option to choose a folder. By default it's a subfolder of c:\program files, but you can chose another folder on another drive if you prefer. All you've got to do: uninstall and reinstall. But I'm not sure DNS does it. Easy to try, however. Note, before uninstalling, make a backup of all files belonging to it!

2. The files it creates after the install, like (I assume) your training vocubulary. I don't have DNS, but I assume it chooses a folder like c:\documents and settings\<your_usernam>\application data\DNS. It might have an option to assign another folder. Or, just as, it might not. Try the options, and read the help.

I can't help about the invalid vocabulary. Maybe get an old version from your backup?