Add ESX 4.1 to Vcenter 5.1

I have 4 ESX 4.1 348481 host and 2 new ESX 5.1 sharing the same storage and network. All the virtual machines are placed on the 4.1 ESX hosts. My Vcenter is 4.

Can I Upgrade my V-center to version 5 and add my ESX 4.1 to it, so that I can move all my virtull machines to my 5.1 hosts??

Best Regards

Mikael