Dhcp client service

i recently updated my msn which caused a problem with the file dhcpcsvc.dll in the system32 folder, this has caused problems with staying connected to the net whilst talking on msn and because of it i have to constantly restart the file, im trying to reset the dhcp client service to fix this problem however i cannot find a way to do this, i have tried making a new file with the same name and putting it in the folder but the file is protected and i cant find anything that would help that can be typed into the command line, does anyone have any suggestions? if it helps i believe the file was corrupted from the installation of the newest msn and some non verified add ons for internet explorer from sun microsystems, a java update of some sort, not sure if that would help or not but the more info the better lol