>I see that when adding a checkbox in a table row, that it requires at least 4 pixels for the top and bottom margins. If I don't have a checkbox in a table row, my row height is less. Is there any way to define a style for the checkbox to avoid that?

I just did a quick play around with
my style:

input   { color: red; margin: -7pt; padding: -3pt }

and my test:

<hr><input type="checkbox" value="checkboxValue" name="checkboxName"><hr>

I really recommend using Adobe GoLive for nutting out GUI problems. I sussed this out in seconds.

Sarah