Before executing a HeNCE program, htool will start a virtual machine. PVM will be started if necessary and any hosts defined in the cost matrix will be added to the machine's configuration. By default, PVM accomplishes this using the system's remote shell facility (rsh command on most machines; remsh on a few others). PVM normally expects to use the same username on the remote machine as on the local machine and expects you to be able to rlogin to all machines in the virtual parallel machine without entering a password.
If this is not the case, the best approach is probably to start PVM manually and add all hosts in your virtual parallel machine before starting htool. You accomplish this by starting a pvm daemon (pvmd3) in the foreground on the machine on which you will run htool. You can supply pvmd3 with a PVM host file. There are options to use alternative usernames and be prompted for passwords. See the PVM 3.X User's Guide for information on host files.
It is possible to have htool start PVM with a hosts file by setting the PVM_HOST_FILEvariable in your .htool file. However, the password option will not work. Other host file options will likely work.