I went through this same nightmare as ESXi 4.1 uses some cryptic version of RHL, and the command set is different than what Dell has documented (you'd think they would have actually tested the commands they documented). Easiest way to update your server is give one NIC internet access and update your BIOS/firmware using Dell's built-in UEFI tool (I think it's Cntrl-F10 when booting). It's painless unless you have to use a proxy to bypass firewalls (which there is a section to provide a proxy if needed).