Well to start with 1 GB is not much memory for an ESX server - first you need to under stand there are three things using memory on you ESX host -
The service console - in essence a VM that helps you manage your VM - this by default is given 272 MB of memory
The Vmkernel - this is what does you virtualization and the memory use will fluctuate as you have more vms
The Virtual Machine - this is the memory used by your VMs
So what you are seeing - The console memory is the service console so you are using 252 out of the default 272 - the remainder is being used by the vmkernel and VMs and that is why you are seeing a utilization of 908%-100%
In regards to the firewall not sure what you are attempting to do - the firewall ports on the service console can either be controlled by the VI Client for a set of predefined ports or from the console command line with the command esxcfg-firewall
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