So, let me retort:
Everything was working fine.
You recompiled the kernel with your own settings.
Everything isn't working fine anymore.
Ok, so i am assuming that everything was working fine out of the box. (what distro are you on??) then, without changing any settings, like say turning of DHCP support in your network configuration, it stopped working after a kernel upgrade/recompile.
Hmm. If all of that is right so far, then you can fix it by simply installing the original kernel package, changing into the directory it's in, doing a make xconfig saving the configuration to a file, exiting, going to the directory the new kernel is in, loading the saved configuration file from the stock kernel, recompiling.
Now here's the catch, this worked for me in Slackware 9.0 and it worked like a charm. (I'll besure to back up my configuration now, before i screw things up ... it's amazing how many things you can back up after it's too late)
Depending on what distro you are using, you might have a config file in the /boot directory of the old kernel (i could be wrong in this).
Going back to recovering your original kernel configuration, i just tried that, and yes it does work, it does however assume that the installed stock kernel is the same as the kernel in their packaged format. If it still fails, think back, did you change any settings relating to your netwrok?
BTW, if you update your profile to state what distro you're on, it makes it easier for us to be more diffinitive (not that it really makes much difference to this problem) .
best of luck, and i apologize for this being less than elegant, anyone else got a better solution, i'd love to hear it
HCP is not needed in your case -- its a kernel based DHCP client. 
