Converting a cd to ISO format can be done with alot of utilities, one of which is MagicISO under Windows; since i use Linux everything is free there and without any copyright protection.
Using ISOs from the network can be done with Daemon Tools for Windows, which acts like a virtual DVD-ROM drive with a .ISO inserted; it creates an additional drive letter where you can access the contents of the CD/DVD image.
Again: after installation it should not matter how fast you can read from the cd/dvd, because its only used for copyright protection not for reading actual data. It doesn't copy 10GB to your harddrive for nothing.
Games in the past would copy about 5MB to your HDD and have all the data on the CD-ROM instead, for example the movies which consume alot of space. But i haven't seen this with any modern game.