You're using incorrect terminology AGAIN. First off, this is disk:
And this here is called disc:
And back to topic. Some solutions have been mentioned. Now the instructions how to do it. Som games may get away with CD requirement just by updating it. Command & Conquer: Renegade is one game which gets away with need of disc when it's updated. So patch the game and try does it work without disc.
If it doesn't work that way, next thing is creation of *.ISO file and running it from virtual CD/DVD drive. Many CD/DVD writer programs can create an *.ISO file from disc in the drive. Next download & install program that makes it possible to use the *.ISO file. Alcohol 120% was mentioned. Another is DAEMON Tools. Run the program, mount *.ISO file, and play the game. If game is looking from actual disc drive, do this: uninstall game, install game again from virtual drive, patch the game, and play the game.
If game has copy protection * that prevents anything from above, simplest solution is to find & use crack. What comes to legality, I'm not lawyer, but in many parts of the world it is legal to create and use back ups regardless what EULA says.
Those who still play games from disk, just copy the bloody thing to HDD and run it from there
You know what they say, don't you? About how us MechWarriors are the modern knights, how warfare has become civilized now that we have to abide by conventions and rules of war. Don't believe it. MekWars