IE prior to 7 has an incorrect interpretation of the box model. That is, margin/padding are treated incorrectly. Further, if you specify the wrong doc type, IE (including 7) will pop into quirks mode and render some things incorrectly. Further, default dimensions for some things such as line spacing are set differently in different browsers. One needs to specifically set the to the desired values.

For additional information, Google "Box Model" or "Box Model Hack".

Since you are learning HTML, you should learn CSS. Tables aren't a good way to determine layout; they're for tabular material.