How to change the markup for a field
If you want to change output of the field in a Views, use Semantic Views

You can also turn on the Theme Developer module, check which .tpl is used to display piece of content you want to change and then create this file in a way you want.

Another modules that provide similar functionalities are:

Quickest solution, just turn this module and forget about drupal's nested divs:

Fences

More complex, this lets you to set up fields markup - for views as well as full node: 

Semantic CCK

The most complex, apart from fields markup, this lets you to set up columns, headers, footers etc. inside of full node view, as well some views integration:

Display Suite