how to use OpenXML with word 2007 template?

Does it have to be a real template? I am asking because that implies some sort of "mail merge" type process, which can't/shouldn't be done on the server.
If you can use a regular Word document,
the Open XML [^] will generate a class for creating the doc in which you can replace the 'template' fields with the real data.

In the generated code, it will look something like this:

Run run1 = new Run();
Text text1 = new Text();
text1.Text = "This is a fake template, and here is the DATA1";
run1.Append(text1);
paragraph1.Append(run1);

but you'd change it to this:

Run run1 = new Run();
Text text1 = new Text();
text1.Text = "This is a fake template, and here is the "+DATA1;
run1.Append(text1);
paragraph1.Append(run1);

And replace all your variables at runtime.