Yeah you don't need to be good at maths to do CSS. A calculator is your friend when messing around with margin, padding and widths. If you want to get stuck into it and want to create compliant CSS/XHTML sites then get a text editor like notepad++ and start coding everything by hand. Wysiwyg editors are useless when it comes to creating professional standards based websites. If you hand code everything from scratch you will get a much better understanding of the code and that will help you a lot when trying to debug sites and solve coding issues.
There are heaps of tutorials online. And the best way to learn is to just mess around with it and learn from your mistakes. There's a lot of trial and error involved when starting out with CSS and you will need a lot of patience (mostly with cross browser issues).
A few sites that can help you:
www.w3schools.com
www.alistapart.com
www.htmldog.com