Where on a windows xp system can you configure the applications suggested under open with for an extension

In windows registry you can create a tree to assign an extension to an application. Take a look at the following answer:

Experts exchange file extension

I don't want to asociate a file type with an application.

In my case its a tab separated value file for which I want to have users see excel as a possible way to open an application.

I know a user can click browse and than select an application so it is listed under the "other programs" but in our case the c:\drive is blocked for access for the users and they cannot browse to excel.exe.