I recently found a program called mdf2iso.
This program lets you convert your Alcohol 120% files to ordinary iso files.
The program is also in the repositories, but that is a version that do not handle big files that well.
If you do have an big file (fex. an DVD), you will have to patch mdf2iso.
The easiest way, if you do want to compile yourself, is to surf to: mdf2iso at berlios and download the source.
To find the patch, you will have to enter this adress.

Open a terminal and type in:
gedit large_file.patch
In this new document, you will have to paste all the text from the patch page, save and close.
Extract the mdf2iso source with the command:
tar xvfj mdf2iso-0.3.0-src.tar.bz2
Now it is time to patch the file:
cd into the mdf2iso directory and:
patch -p1 < /DIR/OF/YOUR/large_file.patch
This should not give you any output errors.

Then it is time to compile, as usual:
sudo make install

To use mdf2iso, simply use the terminal:
mdf2iso /home/myhome/alcohol-dvd.mdf /home/myhome/alcohol-dvd.iso
That should be it..

If you do run into any trouble, I have built a .deb package with the patch already appended.. Send me an message..