If you have Open Office from the official site, then IIRC it will only run if you have an environment known as X11 installed. Most Macs won't have this by default, so you will have to install it yourself from the original install discs. This is a "Linux-like" environment that allows OSX to run unix -designed programmes.

I've never used it, and suspect it's a pain. There should be lots of support out there if you google.

Alternatively, you could download NeoOffice here, which is a slightly older version of OO, but installs directly onto OSX (I think).

Or get a nice copy of iWork.