I know nothing about this and am asking for a friend. He wants an application that he can write music in a staff view and print it. What would you recommend?

Anything but Sonar! Ouch! I know that sounds harsh but the notation in Sonar is not good enough and probably development is dead. Sonar is good for a scratch pad type chart. There are plenty of other alternatives that do very professional looking work but be forewarned, notation programs are pretty expensive! Checkout Finale. It's used by a lot of pros as well as amateurs. I bought Notion 3 here in the Cake store when it was on sale. It really is not that bad but it is 32 bit. I'm sure the other guys can come up with some more alternatives. Someone mentioned a freeware notation program but I don't recall what it was.

  NoteWorthy composer

True, Sonar's notation is truly sad.  The new version of Notion should be out soon and it will be 64 bit.  Sibelius is the best there is IMO.  I have both but I really only use Sibelius.  They have a baby version for about $100.  Notion's edge is that it is simpler and easier to learn since it has far fewer features than Sibelius.  It all depends on your needs.

Thank you. I will pass on the information you gave me

I use the Sonar staff view to edit midi...as a BASIC editor, it works fine.... but as has been pointed out, the Sonar staff view and printing capabilities are more of an afterthought with Sonar. 

If your friend is wanting a serious musical staff scoring and printing program....Sonar is probably not the best choice.  I have heard good things about both Finale and Silibius....

finale.  they have several versions as well.  the cheapest version I believe (unless they've changed it since I last looked) is only $10, but the functionality of that one is pretty limited.  I have the ~$100 version and it does all I need it to do.
 
Avid recently bought Sibelius.  MakeMusic owns Finale and Garritan and other programs.

This will give your friend an idea of what's available:

http://music-notation-software-review.toptenreviews.com/


EDIT: Your friend might find this free (donationware) program useful:

http://musescore.org/en

Finale Songwriter! It's cheap but gets job done. 

http://www.finalemusic.com/SongWriter/Default.aspx

MuseScore... Free and does quite a bit..

Only negative is lack of midi output..