VSZ, Sorry to be the bearer of bad news. The issue is this, the R520 doesn't support 2003 as the host OS. It is supported to install on a VM, but not as the host. You would need to go with Server 2008 to have Windows as the host OS.  Let me know if you have any questions.
Hello! I need to install the Windows Server 2003 R2x64 to P520-dell server and can not find a driver for PERC H710 adapter for this OS. I need to create a floppy disk with the driver to install the OS. Help me please!!   
 PowerEdge R520 (install Win2003 R2 64bit)