I am going to require that you work with a grid for your website. There are many reasons for this, the main one being that it is how every single professional web designer worth his/her salt operates.
First off, here is an informative if annoying video about the subject:
I am going to use the 960 Grid System. and I am strongly encouraging you to as well. It is actually a little outdated, but it is a great way to start for a beginner. We will go over how to use this in class.
Here is a longish video on using the 960: