If you want to give a try to ESX or ESXi on a weaker server or even in a virtual environment such a VMware Workstation (it runs fine on Workstation v7 and v8) you may want to be able to run your ESX without enforcing 2 GB or more RAM memory. I found a great solution how to twaek a boot script here.
The whole page http://www.yellow-bricks.com by Duncan Epping, a Principal Architect at VMware, is definetely worth seeing and I strongly recommend it.
By the way, did you know that „RAM memory” has got a RAS syndrom?
EDIT: Right, but how much memory you will need to assign to your ESXi? According to this guy, 768 MB should be enough. I started to get this rathe unpleasant suprise at less than 1700MB (well, somethin like that, with 1700MB it works, with 1680 it does not; I did not try with values in the middle):