Create office documents on the server

Hi all

I need to create office documents on the server, namely excel and word
documents. However I need the ability to do the following easily:

1)It must be possible to create the docuemnts based on some template,
so that If I modify the template then any newly created documents take
on the look and feel of the template. The template will be created
using word, excel etc. I guess the template wil have a place holder
section where data should be placed....
2)The template will need to have the ability to contain a list of
information, for example the template may display a number of orders,
each order will look the same but the template will define a region
where orders are placed and how they should appear
3)It should be possible to use differerent templates
4)The mechanim used should be scalable and quick.

How can I achive this? What are the options to do this onthe server
using c#, asp.net?

Ideally using free tools or open source tools.....


Thanks guys