Thanks Sheri - your not giving up on this means a lot to me!
Well, as far as I understand from SSD gallery guidelines, layouts are not allowed to be any larger than 150kb. So, the closest my software lets me get to this size, that's how I save them, which is normally at 148 kb. For my personal use of the layouts on the computer, I save them at the highest quality (normally somewhat between 4-6mb, depending).
Now, I just uploaded both versions of my latest layout onto photobucket, as you recommended, and there even the smaller file (saved with web optimizer at 136kb) turns out pretty good, the original file of 4.3mb is stunning in quality! (Just as I'm used to see them on my mac). So you say, there's a possibility to link up those photobucket files with the gallery and get them uploaded this way?
Anyway, thanks a ton, Sheri, I can't believe you keep coming back, trying to help!