The recording equipment has to be something that QuickTime will recognize. QuickTime recognizes almost all major sound cards and built-in microphones.
Some computers come with built-in microphones. These are of varying quality and are greatly effected by where they are located on the machine. Some built-in microphones will pick up the noise of the cooling fan, keyboard and mouse clicks, or other ambient noise. On the other hand, some built-in microphones work exceptionally well for the task.
The best way to determine if a microphone is adequate is to make some recordings with it and listen to the results.
The computer must have a microphone-in jack for plugging in a microphone. For simple voice recordings a simple external microphone will usually suffice. These can be found at any electronics or office supply store.