CUBASE can run as a Midi and sample sequencer to connected hardware players (sometimes referred to as ROMplers) or run a series of VST instruments and applications. VST (Virtual Studio Technology) are numerous and know no bounds! From simple FX units such as compressors, reverb, dealys etc - to full blown Synth engines and drumkits - even Guitar simulators.
Guitar Rig, EZ Drummer and the KORG Legacy set of synths, will get you a long way in laying down a wide variety of instruments at studio quality. Depending on your computer's resources, the sky is the limit - you can even incorpoarting these with REAL hardware instruments and equipment.
Again, click the link for some tailored packages to help you get off the ground using CUBASE: