Alain,

I have a no-budget, a low-budget and a medium-budget solution.

No-budget: Download OneManBand and play the 5 free styles on your PC keyboard thru the onboard soundcard. (Does't take any space either)

Low-budget: Get a second hand keyboard with midi out and a soundblaster and register OMB so you can play a million Yamaha styles.

Medium-budget: Get a good 88-key MIDI controller and a Yamaha SW1000XG soundcard and with OMB you will have an arranger setup that is unrivalled.
http://www.home.zonnet.nl/josmaas/onemanband

JM