after you change your network settings, you may need to restart the affected services (as root):
/sbin/service network restart
/sbin/service smb restart
Also note that all the nework configuration files are located in /etc/sysconfig You may want to back this up before you mess with it (as root):
tar cvfj ~/syconfig.tar.bz2 .
Then later, you can always restore the backups if your networking stops working
rm -rf *
tar xvfj ~/sysconfig.tar.bz2
Its also a good idea to keep a backup of your entire etc directory. I love having backups!
Here's the samba HOWTO