This image looks like it is only for recovering or reinstalling ESXi....per dells web site. I'll do some hunting to see if they have a installation CD.
DELL vSphere Hypervisor 5.1
ESXi 5.1 Recovery Image Build# 799733 (A00) This ISO image should be used only to recover/reinstall the ESXi image to SD Card/USB Key on Dell Platforms.
Eric