CSS by itself is practically simple and uncomplicated to understand. You can find lot of good CSS resources in the internet. Your actual challenge is learning all the quirks and bugs in every browser and this takes a lot of time.
You should absolutely get the time to learn how CSS works, but as a newcomer if you want to get started now, without distressing about many issues, I would advocate using one of the so-called CSS frameworks.
Here are some of the better acknowledged:
1.Yahoo! UI Library: Base CSS
2.960 Grid System
3.Blueprint
4.YAML
5.Bluetrip
6.Emastic
