2
Xoops for Dummies discusses a few ways of handling this. You can either edit the template set, or add a one page module for static content.
Link:
https://xoops.org/modules/news/article.php?storyid=1519
Another option is to use a module like iMenu to replace the default Main Menu built into Xoops.
Link:
http://prdownloads.sourceforge.net/xoops/xoops2-mod_imenu_v2_0_3_luinithil.zip?download