theglanda, неплохо об этом написано в Windows Script 5.6 Documentation:
script56.chmVisual Basic for Applications Features Not In VBScript:
CategoryOmitted Feature/Keyword Array Handling Option Base Declaring arrays with lower bound <> 0 Collection Add&comma; Count&comma; Item&comma; Remove Access to collections using ! character Conditional Compilation #Const #If...Then...#Else Control Flow DoEvents GoSub...Return&comma; GoTo On Error GoTo On...GoSub&comma; On...GoTo Line numbers&comma; Line labels Conversion CVar&comma; CVDate Str&comma; Val Data Types All intrinsic data types except Variant Type...End Type Date/Time Date statement&comma; Time statement DDE LinkExecute&comma; LinkPoke&comma; LinkRequest&comma; LinkSend Debugging Debug.Print End&comma; Stop Declaration Declare (for declaring DLLs) Optional ParamArray Static Error Handling Erl Error Resume&comma; Resume Next File Input/Output All traditional Basic file I/O Financial All financial functions Object Manipulation TypeOf Objects Clipboard Collection Operators Like Options Deftype Option Base Option Compare Option Private Module Select Case Expressions containing Is keyword or any comparison operators Expressions containing a range of values using the To keyword. Strings Fixed-length strings LSet&comma; RSet Mid Statement StrConv Using Objects Collection access using !
VBScript Features not in Visual Basic for Applications:
CategoryFeature/Keyword Declarations Class Miscellaneous Eval&comma; Execute Objects RegExp Script Engine Identification ScriptEngine&comma; ScriptEngineBuildVersion&comma; ScriptEngineMajorVersion&comma; ScriptEngineMinorVersion

При необходимости найти файл script56.chm с данной информацией не составит труда.

Так же поведение и взаимодействие с ActiveX объектами зачастую отличается между VBS и VBA.