Hi Leah,
You have a few options for setting up multiple sites in IIS6.
1) Give each website its own unique IP address. While this works very well, it is "expensive" in terms of IP addresses. It is also completely unnecessary considering the other options. However, if you intend on using SSL, each site with SSL must have it's own IP address (there are ways around this but I don't consider any of them stable).
2) Give each website a unique port and a shared IP address. This method is fine for development but can be very confusing for end users and isn't really viable on the Internet because you can't be sure what ports are available to users outside of your own network.
3) Give each site a host header and a shared IP address. This is my favorite method because it provides the most flexibility. It does require a little bit more configuration but it pays off in the end. I located an article at Microsoft (http://support.microsoft.com/kb/324287) which explains how to configure host headers in IIS 6. You will also need to configure your DNS to point to the correct IP address for each host header (domain) you create. IIS will handle directing the traffic to the correct website.
I can help further if you have questions but I think this should give you a pretty good head start.
HTH,
Joe D.