css gallery theme, wp2.5 thumbnail size

http://www.tronicscribe.com/portfoliosfriend

I’m using the css gallery theme by osdesigner, and on the installation notes it said to use the plugin, ShiftThis | Thumbnail Size. however, I could not get it to work. I uploaded one large image, at 500×344 and I set the thumbnail size with that plugin to be 255 wide. after a while, on the osdesigner forums he said the plugin didn’t work with wp2.5 so I unactivated it, and I tried using the built in wp thumbnail size editor. I set it at 255×144 and ticked the box to force that size. well the thumbnail on the gallery still loads as the large 500px size. I don’t know what else to try, so if anyone is familiar with getting this theme to work, please let me know. 😀

also, just to clarify, the other thumbnails on my main page that are actually the correct thumbnail size, are that way because I had to upload two images, one large one small, so that it would look normal. but I should only have to upload my large image and let the thumbnail scale it to the smaller size.

oh, and for the custom fields I needed to create for each post in this theme, for the field “images” and “thumbs” I used the same url to the large image. except on the posts that the thumbnail’s are correct, I use the url to my smaller image for the “thumbs” field. hope I’m not missing something too simple. I tend to do that. thanks!