Recommended Partitioning/Redundancy

Can anyone spell out some typical disk/volume configs for various servers on an all Win 2000 network? I guess typical volume/redundancy layouts for domain controllers, DNS, web, and mail servers would be good just to see get some good ideas. For instance, our mail server has 5 SCSI drives, 2 Pentium II 400s, 512 mgs RAM, and we were thinking of going with a mirrored volume for the system drive, and a RAID-5 volume using the other 3 drives for the Exchange 2000 installation files, etc. Is this a good idea, or would RAID-5 be a little slow for a mail server?