Select the text box -- and then select the Animations tab of the Ribbon.
Click the Custom Animation button to bring up a task pane of the same
name -- this typically shows up on the right side of the interface.
Click Add Effect -- (from here on the steps are the same as for PowerPoint
2002 and 2003). Choose any Entrance effect.
Thereafter, click the downward arrow next to the animation you just added --
it will be listed in the Custom Animation task pane. In the resultant menu,
choose Effect Options.
In the dialog box that comes up, make sure you are in the Text Animation
tab -- choose to animate by 1st Level Paragraphs if that's not already
selected. You can also play with the other options to see if that works for
you.