Ideal disk setup for Postgresql 7.4?

I help manage an animal hospital of 100-employees Linux servers. I am
new to database setup and tuning, I was hoping I could get some
direction on a setting up drive array we're considering moving our
database to.

They're currently on a two-disk Adaptec RAID1 with Postgresql 7.4.2.

The drive array is a 7-disk fibre channel on a Qlogic 2100 controller. I
am currently testing RAID5 (sw).

The main reason of moving to a drive array is the high level of context
switches we get during the day (>30K for 20 mins per hour). The OS and
database exist on the same disk but seperate parition (which probably
makes little difference)


additional info:

On average, 30-35 vets/doctors are connecting to the database at any
time from 7am - 7pm. The database is very active for the small company.

Server Info:
Centos 3.3 (RHEL 3.x equivelent)
4GB RAM
Adaptec 2100S RAID
Qlogic QLA2100 Fibre

Any feedback/suggestions are greatly appreciated.

Thanks.

Steve Poe