Passing authenticated user creds to infopath form from SP

[sasquatch]

I know this thread is not new, but I also have seen that a variety of
approaches are suggested and I guess I'm not qualified to make a call
as to what will work best for me.

Here's the situation: I need to pass the authenticated intranet users
domain username from the share point site to the infopath form in the
library on form load. I'm running SP services, not portal. Is a script
call in the onload call enough and if so any good examples? Do I need
to install portal?

Thanks!