I have been creating custom gis tools with python via the arcpy module. I can set up the tool successfully with parameters and all, but I cannot figure out how to create help text that shows up on the sidebar of the tool like the standard arcgis tools have.
In ArcGIS Desktop 9.3.1 and prior, right-click on the tool in ArcToolbox and select Edit Documentation. At version 10 it is a little bit different, this thread on Esri Support describes the issue: http://forums.arcgis.com/threads/405-Beta-10-ArcToolbox-Documentation
Specifically, at 10.0, you need to access the toolbox item from the ArcCatalog window within ArcMap 10 - it doesn't work from ArcCatalog itself. Right click on the individual tool, select Item Description, then click Edit.