Adaptec’s page on the card is here:
http://www.adaptec.com/en-us/support/scsi/u320/asc-39320-r/
I grabbed the “HostRAID” drivers here:
http://www.adaptec.com/en-us/speed/scsi/windows/adpu320_win7_2k8r2_x64_v70012_exe.htm
Another issue is that the onboard SATA controller is not supported with anything past Server 2003.You have to enter the BIOS setup and change the SATA controller from RAID mode to ATA Mode.
That means you have to use software RAID in Server 2008/2008 R2 if you are using the onboard SATA connections.
The final issue is the Radeon 7000M video chipset. The Server 2008 R2 disc didn’t seem to include drivers for that. I couldn’t select higher than 800×600 resolution!
The XP/2003 x64 drivers are used for that. You can get them from Dell’s site by clicking HERE.
Dell does not support Windows Server 2008 on the PE 1425 (as you well know, they have no drivers available for it on their website), but inspite of that reality I have installed Windows Server 2008 R2 (x64 bit) on my PE1425 without any heroic efforts, save cracking open the top and hard-wiring an IDE DVD-ROM drive to the system for the install. My USB DVD drive wasn't consistently detected as a boot device by the BIOS.
After install everything worked fine EXCEPT video, which required a signed, 64 bit driver to get better than 800x600 resolution from the odd-ball ATI Radeon 7000m graphic chip on the motherboard. I found a suitable driver here [0] and have had zero issues.
To install the driver you need to follow the instructions and expand the downloaded file, then run the executable - it will install the proper driver. It seems IBM/Lenovo used the same graphics chip in a few of their ThinkServer series servers.
Also, be aware the on-board CERC SATA RAID controller is not supported under WIndows Server 2008, you'll have to set the controller to plain-old SATA operation in the BIOS to detect SATA drives on the internal controller. There is a Dell "white paper" on this [1] (though it doesn't mention the SC1425 it is the same controller/same issue.
Hope this helps, the SC1425 is a nice, solid server - I bought mine used with 8 Gigs of RAM, and pulled the dual SCSI drives & controller in favor of two internal SATA 500 Gig HDs. I am about to go out and get some right-angle SATA cables - the cables I have are too tall when plugged into the MB, and press against the case top. It works, and would probably be fine, but since I plan on relying on this machine 24x7 I want a more "proper" solution. I need a 12" and a 18 or 24" cable with ONE right-angle connector (the connector on the back of the drive should be straight, the connector on the MB end should be right-angle. An 18" cable could be fine, but I may go with 24" to give the cable a bit more slack. The 24" cable is more than twice the cost of an 18" cable, but we're only talking a couple dollars extra...
Best of luck with your server,
Ken
[0] http://www-307.ibm.com/pc/support/site.wss/MIGR-70513.html
[1] http://support.dell.com/support/edocs/storage/RAID/Upgrade/cerc/cerc.pdf