RAID Configuration for 2003 Server

I’m looking for suggestions for a RAID 5 configuration. The server contains 4 SCSI 36GB hard drives and it will be running Windows Server 2003 Std Edition. It will perform the following roles:
– Domain controller: AD, DNS, DHCP
– File server
– Application server (minimal)

This server will have approximately 60 clients connected to it.

Should I use all 4 drives for the RAID 5 configuration or could I install the OS on the first drive and use the other 3 drives for the RAID 5. What would be the best configuration with the 4 drives?

Thanks for any help!