Complete the dialog box by telling Dreamweaver how many rows and columns you want in your table. In the Table Width text box, enter a number that will either be in pixels or a percentage of the page width, then choose the units from the pop-up menu to the right of the text box.

You can also specify other properties. For Border thickness, enter a number in the text box for the size of the border, in pixels, that will be displayed between cells.

For Cell padding, enter a figure in the text box for the amount of space, in pixels, between the content in the cells and the cell border around it.

For Cell spacing, enter a figure in the text box for the amount of space, in pixels, between cells.

You can also tell Dreamweaver whether or not the table should include a Header row or column and where it should be located: Left, Top, or Both. The icons for the headers tell you what each choice looks like.

Click OK and the table appears in the document.

Dreamweaver shows green dimension lines above the table to tell you the width of the table in pixels. The top line shows the width of the table in pixels. Each column shows the width of the column in pixels if you have set a fixed width for the column. Columns with widths relative to the table width show green lines without pixel values.

To insert a table within a table, place the insertion point inside a cell of an existing table, then choose either of the table insertion methods: Insert Table from the Insert Menu or Click on the Table icon on the Insert Bar.

For a much more detailed description of tables go to:
http://www.webthang.co.uk/tuts/tuts_dmx04/newbie_3/dmx04_3_1.asp