I would recommend that you register an alias in DNS and not use the IP address since those tend to change over the life of the system. Set that up, and then extend the web app.
Extend an existing Web application
You can extend an existing Web application if you need to have separate IIS Web sites that expose the same content to users. This is typically used for extranet deployments where different users access content by using different domains. This option reuses the content database from an existing Web application.
Extend an existing Web application
In the SharePoint Central Administration Web site, on the Application Management page, in the SharePoint Web Application Management section, click Create or extend Web application.
On the Create or Extend Web Application page, in the Adding a SharePoint Web Application section, click Extend an existing Web application.
On the Extend Web Application to Another IIS Web Site page, in the Web Application section, click the Web application link and then click Change Web application.
On the Select Web Application page, click the Web application you want to extend.
On the Extend Web Application to Another IIS Web Site page, in the IIS Web Site section, you can select Use an existing IIS Web site to use a Web site that has already been created, or you can choose to leave Create a new IIS Web site selected. The Description, Port, and Path boxes are populated for either choice. You can choose to use the default entries or type the information you want in the boxes.
In the Security Configuration section, configure authentication and encryption for the extended Web application.
In the Authentication Provider section, choose either Negotiate (Kerberos) or NTLM.
To enable Kerberos authentication, you must perform additional configuration. For more information about authentication methods, see Plan authentication methods (Windows SharePoint Services).
In the Allow Anonymous section, choose Yes or No. If you choose to allow anonymous access, this enables anonymous access to the Web site by using the computer-specific anonymous access account (that is, IUSR_).
If you want users to be able to access any site content anonymously, you must enable anonymous access for the entire Web application. Then later, site owners can configure how anonymous access is used within their sites. For more information about anonymous access, see Choose which security groups to use (Windows SharePoint Services).
In the Use Secure Sockets Layer (SSL) section, select Yes or No. If you choose to enable SSL for the Web site, you must configure SSL by requesting and installing an SSL certificate.
If you use SSL, you must add the appropriate certificate on each server by using IIS administration tools. For more information about using SSL, see Plan for secure communication within a server farm (Windows SharePoint Services).
In the Load Balanced URL section, type the URL for the domain name for all sites that users will access in this Web application. This URL domain will be used in all links shown on pages within the Web application. By default, the text box is populated with the current server name and port.
In the Load Balanced URL section, under Zone, select the zone for the extended Web application from the drop-down menu. You can choose Intranet, Internet, Custom, or Extranet.
Click OK to extend the Web application, or click Cancel to cancel the process and return to the Application Management page.
For information about how to perform this procedure using the Stsadm command-line tool, see Extendvs: Stsadm operation (Windows SharePoint Services).