VMotion and 64 bit are two differnt things.

If you need both you need to ensure that both are available on the model(s) that you are looking at buying.

It depends what series you have as only the Intel 7000/71000 series on the 6850 support 64 bit OS. If so you can run 64 bit OS on the 6850 if yo have the 7000/7100 processors but you can not vmotion those guests to the 2850.

Personally unless you have big reasons why you need 64 Bit OS I would roll out 32 Bit. From what I have read unless you are using more then 4 GB of Ram in a guest it doesn't make much of a difference and in some cases can use more memory then a 32 Bit OS.

So if you un 32 Bit it looks like you can vmotion between the 2850 and the 6850. My only concern would be that they 6850 is a much bigger box then the 2850 so don't expect to be able to put the same number of VMs on the box.

Best of luck!

Its (c). The servers you have dont support 64-bit VMs.

Thanks,
Bala.
Dell Inc.

Bottom line for Intel procs is that it must have VT capability and be VT enabled in the host's BIOS to run 64-bit VMs. This article doesn't have ESX included, but it's worth noting.

http://kb.vmware.com/selfservice/microsites/search.do?cmd=displayKC&externalId=1901

For ESX 3.x, you need VT.