IIS Newbie. Need Help Please

Greetings Forum.

I have a total newbie question for you... please be kind.

I have IIS 6.0 installed on a Windows 2003 Server. The server is configured to be a member of my domain, but is a stand alone server. It has a static IP address (192.168.1.101) on the domain and the DNS of the domain has the proper information for it.

I have six different websites set up on this unit (four of them mine, two part of IIS). However, only the Default and Share Point Administration sites (installed with IIS 6.0) work. I have configured each of my four to have a "host header value" that corresponds to the site. The other four follow the following pattern:
1) When I right click in INETMGR on the site and select "Browse," I get a HTTP 403 (Forbidden) error. This happens no matter which credentials I am logged on to the server with.
2) When I try to use IE to browse for the site using "http://192.168.1.101/<i>sitename</i>" I get a HTTP 404 (File not found) error. The directory checks out, and in fact I can right click on the website and select "Explore" and see all my files just fine.

I seem to be missing some newbie thing in setting up my websites on the system. Can anyone please help me?

Update:

When I stop the Default website and REMOVE the Host Header Value from one of my four sites, *poof* the one site now works... But I need all four sites to work, so I need to use the Host Header Value.

Can anyone tell me if this is a DNS thing? Do I need to add records to the DNS for the Host header values, and if so, how and where? We use DNS through our Domain Controller which is a Windows 2003 Server.

Please help.

if your just browsing internally and using http://ip/sitename, don't you just need virtual directories setting up in IIS instead of host headers?