Upgrade to Flash 8 or CS3

I have not been using Flash for a few years but have a new project to do for a client. What I want to know should I use Flash 8 or CS. The client can give me access to Flash 8 and is willing to upgrade to CS if needed. The project involves alot of XML feeds and flash will be used as a frontend display on a website, animations will race across the screen to different points depending on XML values. Which version do you think would be best for this?