You should also take a look at the card driver. Sometimes an old or invalid driver is installed. This can also be responsible for seeing subliminal stimuli. If you have a card with on-board video-RAM (e.g. ATI Radeon or an older RageFury), normally you don´t have to upgrade your mainboard RAM (we use Elsa Erazors, 32MB onboard video RAM, 128MB mainboard-RAM). I´d say you should only take this into account if your videocard shares memory with your mainboard RAM.