This is because you are trying to install a 64 bit OS on a 32 bit supported motherboard. Your server does not support 64bit OS, Please install a 32bit Linux distribution and you will proceed with the installation.
The i5 is 64bit processor.
You need to create a 64bit VirtualBox, which you can do whether your host operating system is 32bit or 64bit, so long as you have enabled VT-x in your BIOS.
Oracle Certified Master DBA
If you are installing a 64bit OEL 5.9 on Virtual Box running on a 32bit Windows Install with a 64bit Intel i5 processor you need to enable Hardware Virtualisation. Generally, this is disabled in the BIOS
See 64-bit guests at https://www.virtualbox.org/manual/ch03.html#intro-64bitguests and hardware vs software virtualization at https://www.virtualbox.org/manual/ch10.html#hwvirt
You could find references to the BIOS settings if you search google.
Hemant K Chitale