WinVista provides a more advanced security method. It means that you need an administrative privilege to access the (root) drive.

If the game directory is located in c:\dagger, move the folder into another location that does not require an admin right.
Right click on the dosbox shortcut and go to "Run as administrator" if you still encounter the problem.

Thank you ever so much, I shall get back to you if it works,
and again, sorry if this is in the wrong place.

It seems to have worked, thank you very much!

I am also having issues with Vista and Daggerfall. I am going to try the suggestion of "Run as administrator", but I wanted to give some details for anyone else who might have problems. First, I was not able to mount the CDROM directly. Instead, I had to create an .iso file from my Daggerfall CD and use imgmount. After doing this, I was unable to run the install at Huge level based on an "insufficient space" error. By changing "-freesize 500" to "-freesize 1500" I was able to get past that. The install then worked, but I was unable to choose my sound settings. After install, I was able to move the .vid files from the arena2 directory of the imgmount to my install directory, which is strange given the problems I had later. I then tried to copy the dag213.exe file and was told I did not have permission. Thereafter, I could not even see in Explorer the directories that I had created is DosBox. I just wanted to post in case someone else has had similar problems with Vista and Daggerfall.