There are two ways that you can do this.
The first is illegal becuase it requires you to change the game programming by using a no CD crack. So swiftly onto number two.
All you would need to do is to make a working image of your game and then load it into the Alcohol Virtual Drive.
There isn’t a general user guide here for Alcohol but basically stick your game into your CD Writer launch copy protection identifying program. (Best is ClonyXXL, need help go here )
Now you know what protection you are dealing with launch Alcohol. Go to make image (top left). Select your drive and so forth. Select the correct profile that you identified with ClonyXXL or another program. Hit next untill the image is made.
Next all you should have to do is to find the virtual drive that was setup when you installed Alcohol. (If not then you can turn it on under the options menu the virtual drive (may require a restart) in Alcohol). Right click on it and select load image and then find your image that you created on your hard disk.
That should be it. A game that you can play without the CD in the drive. Obviously though each image you create will take up approximatly 600mb. Plus if you game requires more than one CD I am not sure if you can change it on the virtual drive half way through.
Hope that helps.