I need two class libraries that reference each other.
Why? One is compiled in C# and the other in VB.NET.
It would be better if I could somehow merge the assemblies programmatically, without requiring external programs or even the extended framework.
Compile your assemblies via assembly linker tool into multimodule assembly.
For example:
http://blogs.msdn.com/b/junfeng/archive/2004/07/15/183813.aspx