You can use most any still image format as a background, including .jpg, .bmp, .gif, .png, .tif, .tga, and others. You can also use any video clip that Vegas can use, such as .avi, .mpg, .mov, .wmv, etc. to produce moving backgrounds.* Right-mouse-button click on the current background and choose "Set Background Media", or simply drag a still image file from the explorer window onto the frame in DVD A.

I'm assuming your ripple question is about Vegas rather than DVD Architect. Some edits you do will change the length of an event, or insert or delete time. Performing a ripple will move everthing after the edit point to line up whatever happens after the edit to take into account the changes you made. For example, if you trim 3 seconds off of a video clip, performing a ripple will move everything after that event 3 seconds to the left to close up the gap that the trim created.

*Not to make a pest of myself, but i have lots of motion backgrounds availabe in my online store.