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I think you should take one page and pull it's code apart until you understand exactly what factor is creating the new size. The conversation as it is going is just too general to locate the problem.
I'd suggest you start by validating the HTML with the W3C [validator.w3.org] -- this might be as simple as messed up table tags.
If you only use GoLive and do not get into the HTML on your own, then this a good reason to choose this moment to move a bit beyond WYSIWYG editing.
One last thought. You haven't mentioned whether this effect is seen just on your machine, or on others as well. If it's just yours, perhpas you re-set the system fonts to a larger size after your re-format.
Fluid layout (or liquid layout)
Accessibility
CSS
CSS Positioning
Percentage widths
Fixed widths
That may not be a complete list, but it's all the applicable concepts I could think of right off the top of my head. Fluid layout is the way to go these days, and you'll find CSS Positioning quite valuable as well.
Also, if you're going to start creating fluid layouts, you probably will want to leave Go Live behind and work in a plain old text editor. I have found EditPad Pro the best, $39.95 for a license, or a freeware version for personal/non-profit use. Building sites in plain text is much more flexible and gives a lot more control, and also allows for clean, lean markup. Besides that, it will be faster to build webpages in text once you get used to it.