If you want free alternatives to those mentioned above, there's a great image manipulation program called 'the Gimp' - you can download it here:
http://www.gimp.org/
Also, a desktop publishing program called 'Scribus', which you can find out more about / download here -
http://www.scribus.net
I've used Gimp a little, and it seems good, although I'm no expert! I've downloaded Scribus, but haven't had much chance to play with it yet, although I've heard good reviews of it - it does produce PDFs that can be used by commercial printers, which is a bonus.
I'm not familiar with Photoshop or Quark, so can't say how these free alternatives compare...other than on price
D