Hello everybody. Nice to be here!
I recently purchased a Mac Mini to get my Home Recording Studio running and I bought Logic Express 7 also. I am however having trouble with this. What I want to do is just get the keyboard up on the screen by pressing Caps Lock, and then play the keys on my computer keyboard to make a sound. However, no sound is coming out. I try recording something, and the notes appear, but nothing plays back. Also, it says No Output in the bar at the bottom. However, iTunes is working correctly, and I can record a real instrument and it plays back fine. Can somebody give me details on how to solve my problem?

1. Open Environment
2. Choose "Audio" from the left side of the window
3. Create new audio object
4. Choose the correct device (for instance "Core Audio")
5. Choose correct channel, for instance "Instrument" if you want to play the Garageband / other soft synths
6. Open Track Mixer -> you can now see the channel strip for the Core Audio instrument track you just created
7. Choose the correct output channels (if they aren't automatically set) and then just above the output channel selection insert the instrument you want to play.
8. Open Arrange and double-click below the existing tracks -> a new track is created. Keep mouse button pressed on the track and a menu appears, choose Audio -> Audio Instruments -> Instrument 1 (or whatever numer the instrument is you created)
9. Play with your keyboard (make sure the keyboard is set to send on the same midi channel as is selected with your instrument) or get some midi data on the track and start the playback.

Sorry...I didn't get that at all. All I want to do is to use my computer keyboard as a realtime midi keyboard in Logic and hear what I'm playing...

Ok you want to hear what you are playing, so what are you playing?

I mean do you have a synth, or a sampler, or a drum machine or what?

If you simply select a channel in the Logic arrange window like GM piano etc then you won't get any sound, there is a bit more understanding required. How much electronic music experience do you have?

Logic does have it's own sounds, 'softsynths', coldharbour was taking you through the setup prcedure for those which will allow logic to generate sounds for you from midi input.

Select an audio instrument track, it looks like you are triggering a GM track that requires outboard midi hardware.