Yeah, not a good idea at all.
You can use a computer keyboard in a pinch to hit the notes, but fingering will kill you, key feel will make you miserable (no weighting to the keys if you are used to an actual piano), and the lack of velocity sensors will make it sound like sh*te.
You need a USB music keyboard controller at the very least, together with a decent synth module for your computer. These can be had on the small side (not much larger than a model M), though that size only covers a few octaves.