If you are planning to buy a piano or a DJ software, before buying try Virtual Piano from ButtonBeats, a freeware which can be downloaded to you system. This Piano can be controlled by your keyboard as well as by the mouse.
The piano is perfectly tuned and hence all the songs can be converted to real world notes. There is huge active community, where in people create new songs and submit it. Upon approval this will be available to the public, and you too can try it out.
You can make your own compositions and submit it for approval, so if you think you have the talent to compose, then you should use this as the platform to create and get feedback from a lot of other like minded, music loving folks.
There is an online version of button beats as well which you can try before downloading the desktop version. And you if want to be a DJ, try the free virtual DJ kit.
The Virtual DJ kit is perfect if you want to throw a party and you don’t have enough money to pay for the DJ. The virtual DJ kit has loads of trance and hip hop tracks integrated and also has two scratch boards.