You will be requiring the below,
1) Single router with two Serial interfaces
2) Pair of Male and Pair of Female Serial Cables.(Those Blue Ones)
3) Configure the Serial interfaces of two routers with same subnet IP i.e. 192.168.240.0/30 and another two routers with 192.168.240.4/30. Give no shut command on serial interfaces.
4) Configure the Fast Ethernets with different subnet IPs and make the PCs default gateway as FE IP.
After the above setup you can whatever testing you want to do.
Regards,
Suresh Jain