performance problem

Dear,

I have a problem the user complain then feel slow while accessing of my
new install Windows Server 2003. The configure as following:

* Server *
Intel Pentium 4 2.8GHz
512MB RAM
Promise FastTRAK 2000 2xATA RAID card
with 2x 120GB 7200rpm Hard disk running RAID-1 (mirror)
Windows Server 2003 OEM + 5 CAL

* Client (type 1)*
Intel Penitum 4 2.8GHz
512MB RAM
ATA-100 80GB Hard disk
Windows 2000 home edition OEM SP1

* Client (type 2)*
Dell Intel Penitum 4 2.4GHz
256MB RAM
ATA-100 40GB Hard disk
Windows 2000 home edition OEM SP1

all client PC were installed Office 2000 SP3 (or 2002 SP3)

case 1 - They said Excel, File -> Open , this action will delay 3-5 seconds
even that folder contain 20-30 spreadsheets.

case 2 - In a 2000+ JPEG folder it takes near 2 minutes if Insert ->
Object -> Create from file (Windows 98/ME only takes around 30 seconds)

both Server and Clients were disabled QoS. Is that any method to increase
the Network speed? Or the problem was Promise RAID-1 system?

Thanks very much,
David