Recently had found some weird issue while we tried to migrate virtual to virtual from Microsoft Virtual Server 2005 to VMware vSphere 4. The import process done successful by the VMware converter, but we realized the network packets get delay while we performed the continues ping test to the virtual machine. the Ping respond had been delayed more than 1000ms in the LAN environment.
We had verified all the network connectivity, resources allocation from ESX host, which confirmed this was not the problem of the infrastructure we setup. We  performed another round of conversion again by powered on the virtual machines from virtual server 2005, before we performed the migration with VMware converter as physical machine mode. The delay ping respond no longer exist after this. We had opened case with VMware tech support and confirm there is not issue on the Virtual Infrastructure we built.

In case anyone of you had the similar experience, I will suggest you to power on the virtual server from Microsoft, and perform the migration process as physical mode.