Thats a very old version, it does not include the "Show In Site Map" option. Upgrading would be desireable but a couple things to be aware of before upgrading a version that old.
1. The latest version of mojoPortal requires .NET 3.5 SP1 whereas your current version only required 2.0.
3. There have been changes to our skinning system that will require changes to your skin.
Note also that unchecking the "Show In SiteMap" (in the current 22.214.171.124 version) also would remove the link from the user site map page. I'm going to add a separate setting for the next version to differentiate between the search engine site map and the user site map.
Hope it helps,