assemblies contain more then one dll an exe and executable 
code

BOTH VB DLL AND ASSEMBLIES ARE REUSEABLE CODE
BUT WHEN YOU CREATE TWO DLLS WITH SAME NAME IN VB
VERSIONING PROBLEM OCCURS IN VB

IN ASSEMBLES ARE INTRODUCED TO AVOID VISIONIG PROBLEM
IN .NET

Assemblies can contain DLL and EXE both. Different versions 
of one DLL can be handeled by assemblies. They overcome the 
DLL Hell problem. Assemblies Contain Manifest and MetaData 
files. These are the seprate files that describes the 
Assembly and its attributes. 

VB DLL is inprocess.DLL run with an exe                   
where as DLL are not self executable. 
we can reuse DLLs .DLL are not platform independent
If we have more then one Versions of a DLL we can face DLL 
Hell Problem.

Assemblies can contain morethan one dll,exe and html file 
and they represents the resources,type definition and 
implementation of those types.

All most all languages support VB DLL(COM DLL).But
assemblies can support only in .Net frameworks..