Unable to get past Enter Password window

[gasport]

I installed Zimbra on my PC and am now trying to install on my macbook. I get to the Enter Password screen and this is as far as I can go. I do not have an administrative password as I did not create one when I installed OS X. If I leave it blank, which I do on the installation of any program, I get the message that the password is not valid. Is there any way to bypass this requirement as I have no password as I mentioned.