zogg, since you are a newbie, I hope you don't mind me saying that you should never lay out your pages with tables. The best way to lay out pages is with CSS styling and free your layout of tables. Yes, it does mean that you don't have the ease of automation out of Photoshop, but in the long run, you can do things with CSS only that you couldn't do with tables, like position whole images, rather than slicing them up, and being able to overlap images and so on, and that's just the design advantage, nevermind accessibility setbacks that table layouts cause etc. etc.
Having said all that, can I ask, are you attempting to center your table? What do you mean by "floating in the browser?"