Pointing Webmail and Postfix Mail Server to Static IP Address

I've already installed Postfix on my two remote CentOS 5.3 x86_64 VPS' and single CentOS 5.3 i386 remote dedicated server and am about to install Roundcubemail as my webmail program. I'd like to point my mail server software and webmail to static IP addresses so I can use SSL/TLS for the mail server (to retrieve email via my desktop email client) and SSL/HTTPS access to my webmail.

I have two VPS' and one dedicated server, all of which have more than one domain name associated with them. I use Webmin as my control panel on all three servers and have them all configured nearly identically. Webmin is pretty flexible in configuring applications; I'm free to install what I want and use what i want how I want on both the server and the control panel. In fact, anything I install on my server can be accessed via the control panel, unlike most control panels so Webmin won't get in the way.

What configuration files and server changes do I need to make in order to point my webmail and mail server software to static IP addresses. Also, can the webmail and mail server programs share the same IP address?

Please let me know if you need further information to help me. The answers that will help me most are solutions-oriented, respectful and clear. I'm a relative newbie so I don't know all the tech terms related to Linux specifically but I'm a quick study with over 25 years of computer and software experience (read: I can go toe-to-toe with Geek Squad and fix a lot of folks Windows boxes and built my Vista 64 box from bare metal) so please keep that in mind, too.

Thank you.

Sasha