My advice-DON'T purchase Norton. In fact, don't purchase any anti-virus and firewall-you don't know how they will work with your system. There is no one size fits all when it comes to computer security programs. What works for me may not work for you. Norton (or any other security product) might slow down one user's computer, and work fine on someone else's system. It would be a waste of your money if you purchased Norton and it didn't play nice with your system.
Before purchasing your Dell, research the options. There are some excellent free programs available.
You can find a list HERE- Freeware Replacements For Common Commercial Apps:
http://www.bleepingcomputer.com/forums/topic3616.htmlChoose one, install it, try it out. If it doesn't work with your computer or you don't like it, try another one.
IF you do decide to purchase a security product, go to the website for the product. See if there is a trial offer. Install the trial, take it for a test run. You'll find out real quick if it's a good fit for your computer.
The main thing is for you to get security on the new computer ASAP. Until you can install a firewall, at least turn on Windows firewall (for XP); if the OS is Vista-whatever is included with that.
{Mod Edit: Moved to More Appropriate forum~~boopme}