If you're just starting out, I'd recommend you look into one of the all-in-one music studios such as FL Studio, Reason, Cakewalk Project or even Kinetic.
They are all very capable of doing what you're looking for right out of the box. Reason perhaps has the better instruments right out of the box, however with FL Studio and Project you can later on add your own instruments and FX as they support VST plugin technology. This way, once you get comfortable and more familiar with what's out there, you would be able to get the specific instruments for your needs.
There are 3 items that you need for what you want to do: A sequencer, a synth and a sampler. All of the software that I recommended includes them all.
I would also recommend you read as much of the music magasines as you can... and although I am in the US, I find the British publications far more helpful specially for beginners. Specifically take a look at Computer Music and Future Music (there is a US edition of Future Music too, but I'd skip it).
In fact every issue of Computer Music comes bundled with a music studio (sequencer, synth, sampler) on a DVD, so you might even go that route and get to making music with just the price of a magazine.