Using the Converge frameworks
This series of frameworks provides a way to show two items merging into one to create a new entity. Some of the frameworks have a place for labels and supporting text. This is a concept that is sometimes difficult to show elegantly. Just using arrows that point inward does not completely convey that a new entity is created.
The diamonds and the oval in the frameworks are separate fields that can be introduced through animation and colored differently than the two contributing forces. If you don't want/need them, just delete.
Refer to the tutorial and the animated example to see how to format these frameworks.
Customizing the Converge frameworks
If you want to change the size/shape of the frameworks, be sure to group them and resize the entire group at once. Hold the shift key down to scale the frameworks so they don't skew. Once resized, ungroup to proceed with other customizations.
Select color from your template's color palette or a complimentary color for the fill so that the frameworks blend well with the other contents. A good tactic for coloring the frameworks is to select several colors, one each for the various fields in the framework; and the colors should be well coordinated so that the fields in finished framework appear cohesive as a whole and complementary.
The point part of the arrow should be semitransparent so the merge can be illustrated and conveyed.
PowerPoint 2007 options
There are a couple of very cool looking formats that can be applied to the frameworks. The drop shadows on the left tend to lift the framework off the page. The bevel format on the right adds volume to the framework. Both add dimension.
You should probably stay away from 3D unless you want to add it to the "1" only. By adding 3D to the arrows and overlying diamond/oval, you are creating a layering effect - not a converging effect. The 3D formatting will actually work against you as you try to illustrate convergence.
Unless you have PowerPoint 2007, do not use the shadows.
Gradients, patterns, and pictures
Using gradients with the arrows is a good option. Notice the series example above: the arrow shafts fade into full transparency. This is particularly useful if you have more text than arrow: fading the end of the arrow will eliminate the end line so you can use more text gracefully. This effect also implies motion.
Check out the downloadable animation scheme. You don't have to get that elaborate. You can just add the arrows as wipes, you can apply zoom to the diamond/oval, and then fade in the background graphic (either the "1" or the upside-down T-shaped field.