hello, can we use different slide size or preset (would be better) in one gallery?

http://robertcouch.net/gallery/gallery-c-0#2 this is the example, what i want to achieve.

in my gallery i have different types of pictures (for exaple: 600x400 and 400x600).

the exaple shows that it's possible, can anyone help me and tell how to do this?

thanks :)