Hello zimbra community

We are a young web-design company and I have the honor to setup our intranet. I've been told to give Zimbra a go. The problem is that I do not have any experience with linux, so please consider this when judging me by my questions.

Atm, I have the following setup to work with.

- A running version of ubuntu server 12.04 64bit
- the installation files of zimbra

When I run the install file, I get the error about fixing my hosts file. All the articles I found include dns splitting, but we have our own dns server running on an internal ip. I made the entries I've found on Split DNS - Zimbra :: Wiki but I still get the same error during installation.

Can please someone give me a hand. I've spent countless hours on this and can't get it to work. I'd really appreciate it.
Chris