You can not rearrange pages/states in Flash Catalyst 1.0; however you can choose which page/state you want to be the default state when your application loads. To do this, right-click on any state in the pages/states panel and select "Set as Default State" from the menu.
The default state is indicated by a small circle at the top, right corner of the state icon:
If the ability to rearrange pages/states is important in your workflow, you can vote to influence its priority in a future version of Flash Catalyst. It is listed on the Flash Catalyst Ideas site here.