By the time XP rolled around, CDROMs were common place.
The older style alternative was to wait for special "hardware update" release of the operating system you wanted to install.
I've installed NT4 god knows how many times. I'm very familiar with the process.
Floppy is the only universal driver the installer can count of having for storage media, besides the media it installing itself. I always thought it would be smarter if this process allowed you to insert a CD temporarily in the same drive keeping the installer in memory.
I have definitely used OS installers that allowed/required CD swaps, though. Maybe Ubuntu at one point? Now that's a slick setup process. Opening Firefox to read the orange site while your OS installs on the same computer is a great trick.