As suggested in JMI's post, a perfectly working method would be to put:

__asm { int 3 };

on the very first line of DriverEntry, and typing "I3HERE ON" in the softice window. typing "net start drivername" will open the softice window (when it reaches the line with int 3), and you will be able to debug the DriverEntry.

when you don't have the source, you patch the first byte of DriverEntry to CCh, remember the old byte. use 'bpint 3' in softice, and when it breaks, you put back the old byte.

remember that if your driver starts automatically at boot-time, and you forget to patch back the byte before rebooting/shutting down, your computer could enter an infinite reboot cycle (unless you have a debugger loader).