Yes, Lightroom generates three image size renditions when exporting a Flash gallery. The gallery will automatically detect the size of itself, and then download and display the largest image rendition it can. If the browser window is resized such that a bigger rendition will fit, it will download it and display it (and start pre-fetching all the larger renditions). When the window is made smaller such that the current rendition will not fit, it swaps to a smaller one. It will not ever real-time scale the images to fit, with one exception. If the gallery is too small to display the smallest image rendition it has access to at native size, it will scale it down to fit.
Well, and actually you could change the "imageScale" param in the style.xml from "fitToScreen" to "downOnly" which would prevent the gallery from swapping image renditions. The gallery would detect it's size at startup, choose the appropriate rendition, and always display that rendition size. So if the window was resized, the same image size would be used, but would be real-time scaled. (the scroll bar on images was not popular and was removed) This is FYI only, as I don't know why anyone would want to do that, unless they were really ambitious and decided to add the bandwidth menus back in (which you could do by copying the associated XML out of an Elements gallery and pasting it into the localText.xml file of one exported out of Lightroom.
FYI, you can change, add, rand emove menus and menu items by editing the localText.xml file...
