Well, Alpha's link to msdn is the best resource for DHTML you'll find out there, finally MS made something that works great! . You can also buy a subscription to msdn (but i won't recomend you to do so... as it doesn't work as well as the online one)

Anyway...

Let's say your table has an id=TBL

To add a row, simply:

var oRow = TBL.insertRow();

You can set any property of the row by using the newly created object:
oRow.className = "cuteRow";
oRow.height = 20;
oRow.whatever = whatever.

Also, styles can be set directly to that row:
oRow.style.padding = 10;

Now, that would be an empty row.. without cells... you have two choices now... add as many cells as you need in a object oriented way:
oCell = oRow.insertCell()

or do a nasty but code saving job:
oRow.innerHTML = "<td><select>blablabla </td><td>blablabla... ";

Anyway, check the online msdn dhtml library for a complete reference of DHTML objects, behaviors, attributes, etc...