You could install a passive tap in between that and the rest of your network and have your backtrack machine sniff from the tap if you want to actively watch everything. I just have better uses for my time.
Something like that is what I prefer.

Doing all the things, You do with smoothwall with bt4 and even more....
...
But will bt4f provide all functionality for that ( will it have enough tools to make the work of smoothwall)????
Or will I have to add some afterwards?