Hi
All your images/clips should be of the same aspect ratio. eg 4:3 16:9 etc, The resolutions are less important as it is simply a case of the higher the better.
Due to the different shapes of your clips/images some will have borders on the left and right, (vertical images) others at the top and bottom (squarer images), as initially ALL the image area is included in the default 16:9 VP frame.
I am not sure about version 3.0 as I have gone back to using V2.41 for several reasons, but if I remember correctly the controls are very similar similar.
In version 2.41 you use the the crop (or, see below...zoom) effect but should realise that in order to get the same aspect ratio for all your clips/images you will naturally have to lose some parts of your images.(sides or top/bottom)
Assuming you want everything to fill the VP frame (16:9) then proceed as follows:
Put all your clips/images on the timeline and then go through them one at a time as follows..
Activate the clip by right or left clicking it.(It will turn blue and preview on the right.)
Left click the "Effects" tab and select the "Crop" effect. Your clip/image will appear on the left of the screen with a red rectangle on it having 8 adjustment points. For the moment ignore these.
Below the image where it says "Keep proportions", select the16:9 option. (you can use 4:3 if most of your clips are old TV or film format) The red rectangle will now change to the maximum possible sized 16:9 aspect ratio. (Note that if your image was already 16:9, you will see no change)
You can now adjust the position of the red rectangle by dragging it (normally up/down) so it contains the part of the image you want.
Note that you can also resize the rectangle by dragging the sides and corners in or out without changing its aspect ration and in effect zoom into a portion of the image. The enlarged area will still occupy the full VP screen.image This is NOT however, a movie "zoom", just a selective enlargment of your image or clip.
Obviously you would need to do this for all the clips/images on the sequence in order to remove the "bouncing" effect you are seeing as everything on the sequence would now be the same aspect ratio.
If, instead of "Crop" you select the "Zoom" effect, then you will see two images on the left, The first image of a clip (top), and last image of the clip.(below)
Again, select the 16:9 option from the options underneath the images and adjust the rectangles (now 16:9 ratio) to reflect the position/size of the start and end of your zoom. As with crop, the VP frame will remain full. This is a very useful function in fact to impart motion and interest to an otherwise static slideshow generated with VP as the speed of the effect can easily be altered by varying the duration of the slide.
Hope this helps
Nat