Hmmm - what happened to the post I wrote before this one, thanking both of you for your quick responses?!! I also explained a bit of what I'd been trying but now it's all gone. Weird. Anyway, the following is my second response to your two posts:
Well, I managed to get rid of the divs with no disastrous results but I cannot use auto instead of 50px. If I change it to auto, the tables snap to the left. The thumbnail grid I can leave with the 50px because it (hopefully) will always have at least 5 thumbnails across. The pedigree table, though, really does need to be auto-positioned because some of the dog names are really long and some really short. The only one I've filled out so far actually had to have no horizontal positioning because it takes up the full 700px width. Others I know will only need 500 to 600px, which is why I want to use auto.
I guess I'll just have to live with the pedigree to the left. It looks awful but I really can't spend any more time fiddling with it.
I have to keep the floats, too, because even after removing the divs, if I remove the floats I can't even see the two tables in Design view. :>(