Need to abort OS X server installation

Hi all,
I have a new Mac Book Pro (OS 10.5) and an X Server - I'm a Windows user but am trying to help someone else set these so the Mac Book acts as a remote administrator for the server. So the server is working and I got my Mac Book working correctly too, however, someone who knows more that I do suggested I needed to install the OS X Server software to get remoted administration to work. (which it turns out I didn't need)

So all was well until I rebooted the Mac Book and the server setup started and I can't seem to cancel the server setup and boot to my old OS. And I don't have a valid license to install the server software on my machine anyway?

Any thoughts other than formatting and reinstalling my old OS?

Thanks

It depends on how far into the install you went. If the install started its progress bar display, you'll probably have to reinstall your OS. Otherwise, you should be able to quit the installer or force power down if necessary.