Migration from esxi 4.1 to esxi 5.1

We have lot of VMs in a ESXi 4.1 (HP DL585) with HP VSA storage. It is being managed using VC 4.1

Now we have installed a new ESXi 5.1 PowerEdge R815 server with New HP4500 storage and it is being managed using VC 5.1

We want to migrate the VMs on ESXi 4.1 to ESXi 5.1

What is the best way to migrate all the VM's from the old to the new enivronment without much of downtime on the VM's.

Is it possible to add or link the old host (HP DL585) to new VC 5.1 and vmotion the VM's? I know I have the option of copying the .vmdk file and creating a new VM on ESXi 5.1. But I am just trying to look of any other ideas for this migration.

Thanks in advance

Regards,