Problems with thumbnails

i have bin following the advance tutorial on this site about adding tumbnails to the existing flash gallery.
The problem is: that the thumbnails come in 2 differend sizes w115xh75 and w50xh75.
wich should then be shown as the thumbnails i want to use.
yet something goes wrong, the thumbnails are shown over each other
but when i remove the photo’s with the differend sizes it works like it should be.
now my question is: is there a way to get around this so i can still use photo’s with differend sizes?

thanks in advance for the help

edit made it a bit more understandable
i wasend explaining it wright:emb: