Photoshop is the king ($640)..
Paintshop pro is almost as good and just 25% of the price
(you can d/l a 30 day trial)
http://www.corel.com/servlet/Satellite?c=Conte nt_C1&cid=1150905725000&lc=en&pagename=uk/Layo ut&trkid=ukgoogjascq406
The gimp isn't as good as psp .... but it's free (www.gimp.org)
photoshop elements is good and cheap but basic ($99)
.... but it depends on your skill level
your example looks easy enough ... but it still requires a reasonable level of skill to do something like this (and a decent package).
You will see amazing examples of artwork done with windows paint ... or a sharp stick ... but these guys are incredibly talented ... and probably walk on water also
Adobe Photoshop is expensive ($640) is a very steep learning curve ...
From your question I assume you aren't a graphic designer ... so don't try to run ... PSP or the gimp are probably worth considering - if only because you can try them for free.
Photoshop Album Starter Edition is also free - but basic
http://www.adobe.com/products/photoshopalbum/s tarter.html