Require fields to be filled out?

The reasons I'd use a userform are:
1) Looks cleaner / more professional.
2) Easier trigger to make sure your whole line is filled out. As is, I can't think of how you'd make sure a whole line is filled.

I've reposted your example with a rough userform. Check out the RowSource property of the comboboxes, and the code behind the whole form to see how it works.

The page I found most helpful when I was creating my first forms was:
http://www.exceltip.com/st/Create_Us...Excel/629.html

Hope that helps!