As TonyBR says. Here are the steps:
Originally Posted by scampo77
1] Open SONY Vegas
2] In the Project Media Pane Import your JPG Movie Poster and AVI into your new Vegas project.
3] In the Project Media pane Drag your JPG to the Workspace. Vegas will create a Video Track.
4] Now Drag your AVI to the same Track as your JPG at a point where your JPG finishes. If you have Audio with your AVI, Vegas will automatically produce an Audio Track for you.
5] Decide how many frames you want the JPG to be and either reduce or increase the JPG by the frame length you want it to be.
You now have your JPG and AVI Events on a Vegas Track.