Hi Emily!
I have a couple of suggestions and I hope others will add to these.
Check out this thread on [url http://webjunction.org/forums/click.jspa?searchID=4195&messageID=12868 ]IT Tutorials[/url]. There are some good recommendations for general Web skills, but the last post has this specific link about css:
"For CSS I recommend WestCiv's online tutorials:
http://www.westciv.com/style_master/house/index.html"
You can also take one of WebJunction's courses. They're online, self-directed, and you have an entire year to get through it at your own pace, or use it as a reference as you work on your css implementation. In the [url http://webjunction.org/do/Navigation?category=442 ]list of online courses[/url], look for the Dynamic HTML course in the Web Development Series section.
Let us know how it goes. CSS is fun!