I recently went back and re-read an article which explained the differences between the <SPAN> and <DIV> tags in HTML.
One thing I seemed to forget was that when using the <DIV> tag it consequently breaks paragraphs. The tag predominantly acts as a paragraph start/end and while you can have paragraphs within a <DIV> you can’t have a <DIV> inside a paragraph.
The primary attributes of the <DIV> tag are:
align (left|center|right|justify)
style
name
More info can be found here: http://webdesign.about.com/library/weekly/aa011000a.htm