The reason for your floating tables to show different on every page is probably due to the fact that float in some way works a bit the same as position: relative and top: 0. So if there is something sitting in it's way - someting for it to base it's positioning on - than that's probably the reason why it's shifting around the pages.
Float is meant to be used together with divisions in the first place, and this is more predictable. I don't know if it's whise to use float on tables, but I wouldn't recommend it.
If you are new to css, you should consider to learn about divisions and tableless layout, as they are more flexible and powerfull than tables and allow for cleaner html code.
As for the positioning problem, I can't give you any advice there, but I think it's best not to use any css positioning on tables, as they don't work together well.
I hope someone who has more experience with tables can help you with this, but I'd personally like to recommend agains using them.