Use the Swap Configuration option to create and configure a swap file, which enables your virtual machines to use more memory than is physically available on the server. For background, see www.vmware.com/support/esx2/doc/ esx20admin_res-memory-manage.html.
You can manage a single swap file with the management interface. ESX Server can manage up to 8 swap files, but you must use vmkfstools to do so.
To change your swap file settings, see Configuring a Swap File.