That doesnt work for this. Already tried that. What version of Firmware are you running?
This is the official HCL version that is compatible
XS31.0081.B06
However, with the newer software updates my xserves run
XS31.0081.B09
I was able to get 1 of 8 of Xserves to run ESX-i 5, and I had to use rEFIt to get it to load correctly. However all other Xserves stall upon loading. Basically right ESXi is about to boot, it just hangs.