Sharing Data - CEO->Division Head->Sales Person

Sharing Data - CEO->Division Head->Sales Person

We are using Professional Edition (seemingly we cant create Data Sharing Rules) - i have default sharing set to Private

We're a small company with two divisions:
1) In Division 1 - the CEO, Division Head and the Sales person are actively working sales together and should be able to see each others Leads and Potentials but the Sales Person can only see his own Leads and Potentials...
How can I set it so that we can see each others Leads and Potentials

2) Division 2 - we want each person to only see their own records, as we're working with partners and dont want data to be shared.

please advise how this can be done in Professional Edition - its a basic feature surely

thank you