Jay,
I'm a dealer who sells both the Casio and Yamaha keyboards.
Here is my opinion. The Casio WK-500 has 76 semi-weighted keys ( a nice feature) and a lot of functions I can get into but not yet. The Yamaha PSRE413 has only 61 keys and is not semi-weighted. The price of the Casio is $299 and the Yamaha is $229.
The main difference besides the number and fell of the keys is SOUND!
The Yamaha sounds are more realistic. Especially Trumpets, Sax's, Guitars, Flutes.
The pianos are both very decent.
The other big difference will be the drum sound quality if you like to play styles. The yamaha is more realistic, especially their cymbal sounds.
The Yamaha also has a couple of knobs that you can use to edit the sounds like a synth. The two knobs can be assigned to abut 16 different paramaters.
The Casio allows you to program different etnic tunings and you can combine different style tracks to create unique new styles, but there are no paramaters to edit the sounds. A plus for the Casio is that it has seperate stereo outputs and stereo inputs and a mic input and the Yamaha only has a stereo headphone jack which doubles as a line output but then the internal speakers are shut off. There is a Yamaha with 76 semi weighted keys call the YPG 235 but it is $339.00.
I hope this helps to shed some light on what the differences would be to someone who is a musician and cares about the quality of sounds.


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George Kaye
Kaye's Music Scene
Reseda, California
818-881-5566
www.kayesmusicscene.com