ESX 3.5 with .vmx
Copy the VMware image to the ESX server, it must be unzipped and untarred. Browse to the data store using the datastore browser in VMware Infrastructure Client (Click the inventory button). Right-click on the .vmx file and choose "Add to inventory"
ESX 3.5 with .ovf
Go to File> Virtual Appliance> Import within VMware Infrastructure Client. Choose "Import from file" and give the path to the .ovf file. Continue with the wizard.