Jonathan,
Server 1:
1. Click NAT
2. Click “+” in the lower right hand corner
3. In the external port range field drag down the list and select HTTP
4. In NAT IP put 192.168.1.90
5. Give your rule a description
6. Check the box which auto-adds the firewall rule
7. Click Save.
Server 2:
1. Click NAT
2. Click “+” in the lower right hand corner
3. In the external port range field fill in “100” for both boxes
4. In NAT IP put 192.168.1.90
5. In the local port field specify “100”
6. Give your rule a description
7. Check the box which auto-adds the firewall rule
8. Click Save.
After both of these have been added click “Apply Changes”
That should get you there.
–Michael I.