With Regards the installation of esxi 5 on mac mini, ive outline the steps below, there were initial problem with getting ethernet working, i have now fixed this. here is an outline of steps so nothing is missed.
Step 1: My Mac Mini Server 2011 came with two 500gb hard drives. i Replaced one hard drive with a 1tb drive and left one 500gb in the bottom half of the mac mini, as i did not want to tear apart mac mini. the 1 tb hard will be were esxi 5 will be installed and mac server hard drive will remain as the primary drive.
Step 2; Installed Refit on 500gb mac Server hard drive. to allow easy booting off usb and allow esxi 5 to be booted from internal hard drive
Step 3: I downloaded the esxi iso image and the broadcom driver which was hard to find. the broadcom driver can be found at the following.
http://downloads.vmware.com/d/details/dt_esxi50_broadcom_tg3_3_120h_v50_2/dHRAYnRAd2piZHAlZA==
unzip the file and place the bundle on your hard drive.
Step 4
i download a program called esxi customiser, to customise installation.
http://v-front.blogspot.com/p/esxi-customizer.html#download.
Step 5
Run esxi customiser, and browse to esxi5 iso and the broadcom bundle driver.
Step 6
Download Unibooting and browse to new customised image and load onto usb stick
thats it, quickest and most simplest way to do this, and now you have coolest esx box in world, all done in less than 5 minutes.