Software Vendor Recommended hardware

We are migrating a oracle system over to a sql 2000 environment in our
finance division. At most, we will have 11 concurrent users attached to it.
This number is usually 4 or 5. The software company is telling us that we
have to have a server with the following configuration:

Dual Xeon 3.0ghz
4g of ram
7 73g 320 10k scsi hdd
(2 hdd mirrored for os, 2 hdd mirrored for application, 2 hdd mirrored for
data, and the 7th drive a auto hot spare)

We think this is way to much server for the application and they are just
using their standard spec they give their big customers. I understand that
the more drive heads the better for I/O, but it also brings in a big cost
factor. How do we determine what we really need in hardware prior to
install? Are there any guidelines for determing hardware requirements prior
to installation?
.