msxml DOM API and character entities

Hello, I need some help
I have some problems with character entities.I am using msxml3 DOM API
Basicly I have to perform 3 steps:

1.Read some text, create and add it to a node
<textnode>This is a test </textnode>
2. Add a character entitie to that node
<textnode>This is a test &en_test; </textnode>
3. Add some text to that node later in my code.
<textnode>This is a test &en_test; New Text </textnode>

I am having difficulties with the 3rd step. I am using the createEntityReference method to add the entities but how do I add more text to the node and preserve the format of the entity. I need this to work badly.Someone please give me a hint ?!