problems with AssemblyBuilder

[ginnone@gmail.com]

I dinamically create an assembly like this

AssemblyName assemblyName = new AssemblyName();
assemblyName.Na me = assemblyNameStr ing;
AssemblyBuilder ab = appDomain.Defin eDynamicAssembl y(assemblyName,
AssemblyBuilder Access.RunAndSa ve);
ModuleBuilder mb = ab.DefineDynami cModule(assembl yNameString + ".dll",
assemblyNameStr ing + ".dll");
TypeBuilder tb = mb.DefineType(" ItemClasses." + itemClassname,
TypeAttributes. Public | TypeAttributes. BeforeFieldInit );
......

At the end, I can save it to disk by using ab.Save(path)

but how can I save it to memory?
and how can I load it in the current application domain? if I try to
load it by using for example
Assembly ass0 = Assembly.Load(a ssemblyName);
i get an exception saying the file cannot be found...