A full CD is about 650MB of data. Todays computers have hard drives well beyond 40GB (4000MB). Let's assume you have at least a 20GB hard drive.
What you need to do is create a folder on your hard drive and copy every single file and folder on the CD into the newly created folder.
Now run SUBST. this is a DOS program that creates a drive letter which represents a folder.
If you copied the CD to lets say mycd in the root of your hard drive, then click on start, run, and type subst G: c:\mycd and press enter.
If the contents of the CD dont appear under the new drive letter, go to start, run, and type G: and press enter.
You may have to change G: to something else followed by the colon if the G drive already exists.
Now, go to the registry if your game is for a 32-bit windows OS and do a search for D:\ and replace D with the drive letter of the CD-ROM drive you used when you installed the game. Change D to G (the new drive). If you are unsure whether to change a certain entry or not, do it anyways. If you see any that start with c:\, ignore them, because they relate to the system.
Do the same to the INI files created by the game.
I still think it is better running 1/2 the game off the CD.