What up man.
This is a pretty general question, but I'll try to help you out the best I can. Using a keyboard is a great way to start making beats. It seems that most people are beginning with Fruity Loops and Reason on their computers nowadays but I still think keyboards and drum machines is also a good way to start. Learning with keyboards and drum machines makes you do a lot of the work on your own. You start from scratch, find your own samples, pick your drum sounds to sequence, and even play out your own melody.

I don't know exactly what Yamaha keyboard you have, but I've always been a fan of Yamaha sounds. All the Yamaha keyboards I've worked with have had the same feel to them. They aren't as soft sounding as Korg or Roland, and at the same time, they aren't as rough as Kurzweil or EMU. They have a big rich sound for whatever type of beats you want to make.
Also, if you have a sampler built into your keyboard, you have a lot more options.

So, to answer your question, using a Yamaha keyboard is definately a good start. After you make a couple hundred beats on that, I would buy a MPC. The MPC will take your drums to the next level, and if your making rap beats and hip hop beats, using a MPC is a must. Although a Yamaha keyboard is a good start, using only one keyboard can't ever acheive the depth you want to have in your beat. Its a never ending road of buying more and more equipment to get to the sound you want, but it will be worth it in the end.

Keep up the beatmaking homie, and remember the key ingredient, don't stop!