Terrible performance on Cerc 6 1.5 Raid 5 card

Ive put a server together for media streaming, with some old hardware i had lying around. These are the specs:

Asus A7N8X-Deluxe 1008 bios
AMD2500+
1,5 GB DDR400
Realtec 1Gbps LAN
Dell Cerc 6 1.5 RAID ( 6 poorts sata oem dell with latest firmware ) ( same as adaptec 2610SA?)
3x 1TB in raid5 ( 1x hitachi, 2x samsung )
1x 750GB hitachi
Windows Home Server with power pack 2 and all updates

Now after some trouble ive created a RAID5 array with the 3 1TB disks. Did this from the bios (dont know if theres another way). Largest file size and with read cache enabled, everything else standard.  After about 48 hours the rebuild and check was completed and got Windows Home Server (WHS) installed on the array. Now everything is working fine. After the install i updated the drivers for the motherboard and lan card, and installed the updates for WHS. The server is connected via gigabit  to a Netgear WRT Router using a CAT5e cable.

First thing i wanted to do was copy my files. But here is the problem, because its incredibly slow. Using Teracopy it shows a transfer rate of 2-7 MB/sec. Both the main pc (quadcore, 4gbram etc) and the server dont have any other processen running. After this result i decided to benchmark the disks using SisoftSandra. With the write benchmark i get the error that the disk must be empty. With the read benchmark i get a combined speed of 35MB/SEC.. Thats slower then a single IDE drive..

To check the raid array in WHS, i tried to install the Dell Openmanage software but i cant run the setup on WHS. The setup states that im not using a compatible OS. Since WHS is Server2003 with some extra's this should work... Also tried the Adaptec management software, and this program will actually install but wont recognise the RAID controller..

So now im about ready to trow this thing out.. Ive build this thing to stream 1080P video across the network, and the specs are high enough. But this just isnt working, the transfer rate is slower than my usb drive. So right now its faster to copy it to usb and walk to my media center...

Any ideas are much appreciated!