Did you try making these in a 16:9 scale? IRFANVIEW might help here.
Bob
I want to create a slideshow that could be played on a HDTV (1080p)directly from a usb drive. The problem is that my pictures are in 4:3 and the TV plays in 16:9 ratio. If I play the slideshow directly it doesn't fill the screen leaving black bands either on top and bottom or on the sides. If anyone has a solution for this please let me know.
Thanks!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic