Shim,
While you could use sounds on your laptop for LEAD/Melody sounds it will be of little use for anything in Yamaha styles. Most Yamaha styles require a XG sound set.
I have not found any of high quality yet.

You might just as well upgrade your keyboaed also, as high quality sample sounds for PC are not cheap. All the good ones are pretty high. Not saying there is none...but my experience is the good ones are high price and require some pretty good PC performance and memory to work well.

Lee S.