The ArchiCADwiki site has released a very useful tip on its website, outlining lots fo different topics relating to linetypes. It covers:

• Available Line Types
• Line Appearance
• Line Weight Display
• Custom Line Types
• Create Symbol Line Types
• Import Line Types from another ArchiCAD project
• Import Line Types using *.aat format
• Import Line Types from an AutoCAD project

The tip can be found here.