How to insert values into C# Dictionary on instantiation?

There's whole page about how to do that here:

http://msdn.microsoft.com/en-us/library/bb531208.aspx

Example:

In the following code example, a Dictionary<TKey, TValue> is initialized with instances of type StudentName:

var students = new Dictionary<int, StudentName>()
{
    { 111, new StudentName {FirstName="Sachin", LastName="Karnik", ID=211}},
    { 112, new StudentName {FirstName="Dina", LastName="Salimzianova", ID=317}},
    { 113, new StudentName {FirstName="Andy", LastName="Ruth", ID=198}}
};

Dictionary<int, string> dictionary = new Dictionary<int, string> { 
   { 0, "string" }, 
   { 1, "string2" }, 
   { 2, "string3" } };

You were almost there:

var dict = new Dictionary<int, string>()
{ {0, "string"}, {1,"string2"},{2,"string3"}};