I would suggest starting out with the tutorial. It does a good job of showing you a sample presentation while letting you try out the interface. One other thing I would do is download a copy of your presentation and bring it on a USB stick, just in case the Internet isn't working as it should.
The key is just to start playing with it (after the tutorial). There's also sometips out there to help you convert video that is compatible with Prezi. You'll sometimes need toupload it to YouTube and then download the convertedvideoto upload to Prezi. Feel free to contact me directly if you have any struggles in this area.
I have used Prezi numerous times and really love it. I don't use PowerPoint anymore unless I have to. I even use it for things such as vacation pics...I put all the images on a Prezi and send the url to friends and family. They can explore, zoom in, etc.
There is a learning curve but you will get the hang of it. I think it's better to get all of your content and then add the paths to determine your presentation order.
You know what's really great? Prezi and a Smartboard. It's a perfect combination and fantastic in the classroom.
A Prezi tutorial that I found useful was http://www.youtube.com/watch?v=M0kriH9dKzk. It's called ice cream for everyone! I've been using Prezi for about 6 months now for P.D. and I showed it to all of my classes last semester before they were scheduled to do presentations of their own. Many of the students used Prezi and the sheer wow factor worked to their benefit. Another tool you might want to try is called pptplex. This free add on to powerpoint allows you to do many of the things yo can do in PRezi from within powerpoint (such as grouping things contextually). It can be found at http://www.officelabs.com/projects/pptPlex/Pages/default.aspx and, after installation adds an icon to the ribbon in Office 2007. The website includes videos that show how to use the tool.
Either way, your presentations are sure to stand out!