Dont worry about the css and your use of tables it looks relativly good and seems to work, that is something you need to decide before you start.
The top navigation needs more evidence that you are hovering, at the moment it just has an underline that you can barely see.
The margin on the left with the member login grey border looks to be indented roughly 5-10px but the text on the right side seems to end about 40px before the header this could be looked at also.
Seems a nice product also, good idea to crudely advertise it on here

v1ck.