Using BSD as filter

[Dave]

I am interested in using BSD on a computer between my cable modem and a router which is both wireless and hardwired. Is this something that anyone could advise me of such as:
    1) Which bsd software would be best for my purpose.
    2) I am interested in what the minimum speed and required memory might be to ensure the computer would not be a bottle-neck on the data coming in.
    2) I am interested in using a different email software instead of Outlook Express. Does BSD have one available or could one be recommended?
    3) I am interested in other software that would work with BSD also.

Please contact me at demeador at cox.net

Dave