Well, I'm definitely not an expert here, and I haven't tried to install X11 and OOo yet (I will, though), but here's a guess:
The OOo web site says that before installing X11 and OOo, you have to install Apple's Mac Developer Tools.
I may have read somewhere that it is important (or at least desirable) to make sure it is the latest version of the developer tools (December 20002), too. The tools come on a separate CD with Jaguar, or you can download them here:
I repeat, I'm just guessing, and would be happy to be corrected by a more knowledgeable reader.