[CentOS] Poor RAID performance new Xeon server?

I have just purchased an HP ProLiant HP ML110 G5 server and install ed 
CentOS 5.2 x86_64 on it.

It has the following spec:

Intel(R) Xeon(R) CPU 3065  @ 2.33GHz
4GB ECC memory
4 x 250GB SATA hard disks running at 1.5GB/s

Onboard RAID controller is enabled but at the moment I have used mdadm 
to configure the array.

RAID bus controller: Intel Corporation 82801 SATA RAID Controller

For a simple striped array I ran:

# mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sdb1 /dev/sdc1
# mke2fs -j /dev/md0
# mount -t ext3 /dev/md0 /mnt

Attached are the results of 2 bonnie++ tests I made to test the performance:

# bonnie++ -s 256m -d /mnt -u 0 -r 0

and

# bonnie++ -s 1g -d /mnt -u 0 -r 0

I also tried 3 of the drives in a RAID 5 setup with gave similar results.

Is it me or are the results poor?

Is this the best I can expect from the hardware or is something wrong?

I would appreciate any advice or possible tweaks I can make to the 
system to make the performance better.

The block I/O is the thing that concerns me as mostly I am serving a 
650MB file via samba to 5 clients and I think this is where I need the 
speed.

Plus I am hoping to run some virtualised guests on it eventually, but 
nothing too heavy.

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