The easiest way to run Haskell software from a C program is to give the
shell command:
runhaskell Foo.hs

I'm a newbie but not that new :) I really have to be able to interpret the Haskell from within the same process.

A more advanced way is, to link Haskell libraries by means of the foreign
function interface (FFI) [1].
There are several tools to support FFI development [2]. I am sure my list
of URL's is not complete.

[1] http://www.cse.unsw.edu.au/~chak/haskell/ffi/
     http://www.haskell.org/haskellwiki/FFI_Introduction
     http://www.haskell.org/haskellwiki/FFI_cook_book

[2] http://www.haskell.org/haskellwiki/FFI_imports_packaging_utility
     http://www.haskell.org/haskellwiki/HSFFIG

My understanding is that FFI helps you to call into other languages from Haskell and vice-versa. I will definitely need this, but what I can't figure out how to do is to invoke the ghci or hugs interpreter programmatically, in-process. I didn't see a way to do that in the links you listed, am I missing something?