I use garageband - a great program. Also, as far as your keyboard goes(assuming it is a digital keyboard), if it has a USB interface, use that. Otherwise, you can get a USB/MIDI converter for not too much on ebay. I recommend the midisport uno, it works great and is very easy to use and set up!
Now, as far as your guitar goes, if it has an audio pickup in it, just use a 1/4" cable and a 1/4" to 1/8" adapter to plug it into your microphone jack. If it doesn't have a pickup (or you are using an acoustic piano), you can either use the internal mic (not recommended) or get an external mic and the appropriate adapters to plug it into your mic jack as well.
Hope this helps!