ifconfig should be at /sbin/ifconfig so go try that first.
If that works then it's probably not in the path for root. When you switch to root make sure you type :
The dash is important.
If that doesn't work then I've no idea what's happened.
I don't know about your icmp socket woes.
I have a linksys "ethereverywhere" (tulip) card which works fine with FC4. It got picked up by the install process and I never had to do anything with it. I actually reinstalled FC4 on a machine just to get this card working (rather than messing with all the downloads and installs :-) ).