Pretty sure you need a dedicated GPU to run solidworks, how much you have to spend depends on the complexities you are modelling. Had to spec up a possible replacement one for someone at work and it wasn't cheap (obviously this was for a decent but not over the top one - entry level Xeon and low-mid Quadro FX).
Not sure what Solidworks is like running on mainstream GPUs, but I've heard it runs ok, but obviously is not supported and some features might not work (eg. realview) without a supported card like a quadro or a firegl.