I thought that there is already such function expression like RANDOM but in UG it is written that its range 0-1 .
One possible solution:
BO.password=BO.ID+x where x any number (ex BO.ID+10102)
To attach rule that will send email to newly created systemuser i think this will work:
If BO IS NEW then
BO.RegState='New'
If BO.RegState='New' then
SEND message TO BO
BO.RegState='Notified'