You can find the dtcpclient in ports/net/dtcpclient under FreeBSD. So, if you are using FreeBSD, it is better to use the ports for installing the dtcpclient.
You can install the dtcpclient easily by running `make && make install' even when you don't use the potrs.
The rc script will not be installed. You can find the rc script for NetBSD. If you are using NetBSD, copy the script into /etc/rc.d as dtcpclient. Don't forget to set execution bit. If you want to run dtcpclient in daemon mode under other OSs, you need to copy dtcpclient.sh and custmize it appropriately.