Forum Moderators: not2easy
However, sure you can. It is not required, but best practice is to declare width: to floated elements. You can use percentages to avoid absolute widths and the containers will be fluid.
My recommendation is to markup the skeleton or framework and then finish off the design. If you run into trouble, post the test ready code that replicates the problem and we will look at the options.
Be sure to declare a DTD and validate the markup. That will avoid, eliminate, or rule out many problems.