This is just a SWAG, but the problem sounds familiar.
When you select pictures for a slide show they are normally in landscape mode and they typically have an aspect ratio of 4:3. This is becaue most digital cameras have most of their available sizes in that ratio (e.g., 1600 x 1200, 1024 x 768, 800 x 600, etc.).
So, when your slide show is created using VCD, the video images sent to the TV are expecting the TV set to have the same aspect ratio of 4:3. However, most of the DVD players, which play either the VCD's or the Movie DVD files are designed for the new 16:9 aspect ratio of HDTV.
However, my DVD player has a switch that allow me to play everything in either format, 4:3 or 16:9. If you look around on your DVD player you may find a control or button or menu selection that changes the format between 4:3 and 16:9. Set it to the 4:3 mode.
On my player that button is labeled "Wide", and when you press it, the aspect ratio toggles between the two modes.