Question : Audio production software for Mac OS X

Someone I know wants to start an online radio station (or at least a music stream) and is looking for appropriate Mac software to mix the music together with jingles and an occasional commercial.

So it is just mixing audio that is already made, with desired goal: an online audio stream (not run from the program) ready to use. I heared that Adobe Audition is good for this kind of work, but that is available for Windows only.

Any suggestions from you experts here? Is Apple GarageBand useful for this? It doesn't have to be a high end expert application, but not too simple either. It should be able to manage a few thousand songs.

Answer : Audio production software for Mac OS X

Then I would recommend that you get Garage Band (Purchased with iLife for $79.00)
http://store.apple.com/us/product/MB966Z/A/iLife-09?fnode=MTY1NDAzOA&mco=MTM3NDc5MjU

FastTrack ($99.95) - is a great audio interface that can take standard microphones so that you can upgrade to a higher quality mic later if the need arises.
http://store.apple.com/us/product/TB084LL/A?fnode=MTY1NDA3MA&mco=MTA4NDQwNDc

And pickup a good Mic Like a Sure SM58 ($99.00) from any music store like SamAsh

Total Cost - $279.00

Or you can skip the FastTrack and Mic and just get a direct USB Mic like the BlueMicrophones Yeti ($149.95)
http://store.apple.com/us/product/TY115ZM/A?fnode=MTY1NDA3MA&mco=MTYxMTI1MzQ

Total Cost Option 2 - $230.00

If you want a little more advanced features for mixing audio you can use Logic Express which will increase either cost by $120
Or even More Advanced - Logic Studio - which would probably satisfy your needs for a couple of years until you really want to go pro.
Logic Studio is $499 - increasing the overall cost by $420

Why these products you ask?
Garage Band - pure simplicity and ease of use - install it and just follow the easy to understand visual controls - but I've still mixed multitrack recordings and created great quality mix downs with it even though it's not a Pro Level tool.
Logic - allows for plug ins and has the ability to control consoles and some midi instruments - but the learning curve is much larger if you aren't familiar with audio mixing consoles and effects patches, plug-ins and external decks etc...
Log Pro - Very widely used - probably the next best thing to investing $10,000 and up on a full blown Pro Tools rig
FastTrack and Mic - just allows for a mixture of instruments/external decks/microphones so it gives you a little versatility

BlueMicrophones Yeti - Like Garage Band in it's simplicity - just plug it in - launch Garage Band and start producing - For $230 the combination of this mic and Garage Band couldn't get any more simplified and easy to use.

My optimal Choice if I was recommending to a friend that shared the same information you have shared with us - would be to purchase the Garage Band - FastTrack and a Sure SM 58 microphone - Total Cost - $279.00
This is the perfect combination of simplicity and versatility.
I've even recorded a live piano session just using my laptop / FastTrack / SM 58 combination through Garage Band and it sounds like a professional recording session.

Good Luck!