PowerPoint can be used to create clickable wireframes

PowerPoint can be used to create a working visual representation of an application with links that are clickable and which then take you to the resulting screen (another slide).

 If you took a screen shot of the Google search page with a query for "space", you could put that on one slide. Then you could take a screen shot of what the google results are for 'space' after you clicked "Search". Then on the first screen, you could use the following process to make the area around the "Search" button clickable and take you to the next slide with the search results, so it feels like you are actually performing the search.

Have something you want to click on, like a link or a 'Confirm' button.
Insert a shape from the toolbar (probably a rectangle or circle/oval).
Make sure it is filled (otherwise it won't be clickable).
Set it to transparent.
Then move the transparent shape over the button or word you want to click.
With the transparent shape selected, click on 'Insert' then 'Action'. You can then choose what you want clicking on it to do.
You can select another PowerPoint slide from the list of things, like playing a sound, etc.
So clicking on the 'Confirm' button you created, will then advance the PowerPoint slideshow to another slide that has the resulting confirmation screen.

During a presentation, the cursur will turn into a finger and allow you to click on this.

You can then have the invisible shape clicked on,

Office also has dropdowns and stuff you can add to make it look like an application. It's recommended that you use the Active X ones so you can move them around more easily. You will have to add the 'Developer' tab to see them. See the link below to see how to turn that on.

http://msdn.microsoft.com/en-us/library/vstudio/bb608625.aspx