It should just be
import [namespace]
for common .NET libraries and namespaces, such as System
to use additional assemblies, first need to import clr
then add a reference to additional assemblies
import clr
clr.AddReference("System.Xml")
from System.Xml import *
Take a look at
Also, have a look at where you installed IronPython. There is a lot of detail in the Tutorial.htm that can be found in \IronPython 2.0.1\Tutorial\Tutorial.htm
You generally create instance of classes like so
from System.Collections import *
# create an instance of Hashtable
h = Hashtable()
from System.Collections.Generic import *
# create an instance of List<string>
l = List[str]()