Inquisit is an open-ended programming platform, so it is theoretically possible to design an experiment that would exceed the capacity of the most powerful computer on the planet. As a simple example, your experiment could attempt to load and present a billion images, each of which is billion pixels in heigth and width, which would easily choke even the best machines rolling off the production lines at Dell, HP, or Apple.
Generally speaking, if your experiment involves lots of pictures and/or video, you'll want to have a decent graphics card along with enough system RAM to buffer all of the pictures used by the experiment. If you are using speech recognition or voice key input, or you are presenting audio files,
you should invest in a decent sound card, along with enough system RAM to buffer your sound files. Otherwise, if your experiment involves little or no media files or audio streams, the minimum system requirements should be more than adequate.