Is the keyboard MIDI compatible, either through a MIDI jack or USB?
How much are you willing to spend?
What kind of sound card does your computer have?
I have tried Cakewalk Project 5
Propellerhead Reason
Ableton Live
I would say these programs are not anywhere on the easy to use side, but with trial and error all are pretty good. The easiest of the 3 was Reason. These might be a little more than you are looking for though.
The sound card on your computer is probably the most important thing. If you have a cheap soundcard you will have latency between the keys and the program which really sucks.
For a "quality" cheap recording sound card you may want to look into this:
M-audio Soundcard
This will also give you a MIDI in jack.
I have a light version of Ableton Live that I can mail to you for free if you want it. It came with a preamp I bought and I have no use for it.