how to install win2k3 64 bits on dell gx 620

I am trying to install win2k3;ee 64 bits on Dell gx620, although it shows on dell site that this hardware is not supporting the o.s but someone from my company already installed 64 bits on the same server, i just reinstall it with 32 bits. but i want 64 bits on this server, pls help.

regards,
sachin