Hi rock,
Not sure if you had a chance to read the help files.
Here's the link for the REW files, and
here's the link for the BFD itself.
You won't need an external sound card if your existing card has a line out and a line in -- but you can't use "mic in" for the input. As long as you have line out and line in, it'll most likely be fine.
Have a look at the help pages and let us know if you have any questions.
Good luck!