You will need to do it in iMovie, just launch iMove, file new project, then click the Aperture Videos icon find your files then drag them to the top window save your project you are done. Take a look at this link, http://www.apple.com/ilife/imovie/what-is.html
In Aperture the only way to combine movie clips is to create a basic slideshow, but you will get better results (stabilization, effects, etc) in iMovie or Quicktime 7, if you have it.
- Create a slideshow with the "Classic" theme: Select the two video clips in the Browser and use: File >New > Slideshow
- Set the Default Slideshow settings (Transitions, Text, background) as you like them.
- Arrange the clips in the Time Line in the order as you want them.
- Press the "Export" button in the upper right corner to export a new video. Reimport it to Aperture.