AFAIK this is simply a HP Proliant DL380G3 with a Cisco OS
Assuming there is nothing fundamentally changed in the BIOS to make it anything other than a DL380G3 then you can install Windows 2003 32 bit
Easiest way is to download SmartStart from HP's site, burn it to CD and boot from this, it will install the OS from your own Windows media but will handle all the drivers for you.
Once youve done that download the latest Proliant Support Pack (PSP) for Windows 2003 and apply that too
I'd try to update the firmware/ROM on both the server and array controller too (online flash is easiest way to do this and is done from within Windows)