The first thing is to decide whether you want to get a basic website up, go with a CMS (Content Management System) or use plain old HTML (or PHP, or whatever you’d like to use).
NickE mentioned Google Sites. That’s definitely a solution if you just want to get a website up without hassle, but I can’t imagine it’ll score many points with the judges (though it’s not something I’m certain of), and it’s not a super-great solution. It can definitely make a website, though, so if you really can’t do much hardcore website work this may be the way to go.
If you want to use a CMS (Content Management System), your main choices (though there are many more!) are WordPress, Drupal, and Joomla!. Wordpress is probably the simplest, and it will let you create a very decent-looking website if you put some time into it. CMS simplifies editing and updating your website, but I’m not sure what FIRST judges thing of websites with this sort of framework (our team has never used one). I’d have a hard time thinking they’d look down on it, since these are used in many, many modern websites today and are very relevant in the web design world (and FIRST is all about preparing for that sort of thing).
The alternative is to hand-code a site, which for you will actually be hand-coding since you lack Dreamweaver or Expression. (I can’t say anything about KompoZer, since I use Dreamweaver for all of my sites, but you might as well try it.)
If you have the time to actually learn some code, I suggest you visit w3schools.com. They have an excellent guide to HTML and CSS, the building blocks of websites, along with other important components like PHP and JavaScript.
In any case, you’ll need to design graphics for the site, which means you need a graphics editing program. I used Paint.NET before purchasing Photoshop, and if you learn to use it you can do a fair amount with it. I’ve also heard very good things about GIMP, another free image editor, which is more popular than Paint.NET (I’m actually not sure why I never used it).
Finally, if your team has some money to invest in web design software, and you’re going to use it, I recommend checking out Adobe’s Web Premium Student and Teacher suite; it’s insanely cheap compared to the standard versions (this is how I afforded mine), but it is still around $450, which I know is pretty steep for a robotics team when you have other costs to worry about. At any rate, the option’s always there if you have the money.
I’ll follow this thread for a while to answer your questions, and I’m sure if I can’t answer it someone else here will be able 
Good luck this season!
-pSYeNCe