DataArchitect is the data modelers' workbench - equivalent to original PowerDesigner. It includes the CDM and PDM, plus the new customizable reporting and basic MetaWorks repository capabilities.
AppModeler is intended for application developers who need to see (and perhaps modify) the relational schema and DDL as well as generate application code. AppModeler includes the complete PDM, PowerBuilder code generation, and basic MetaWorks repository capabilities. AppModeler code generators for other development platforms (Visual Basic??) are expected to follow.