As a part of the broad initiative across Microsoft to support 64 bit versions across many of its product lines, the next release of OCS will support 64-bit operating systems only. This decision will help meet customer demand and is a natural progression of the product that aligns with the same approach taken by the Exchange team (with Exchange 2007) and the SharePoint team (with SharePoint 2007) to support 64 bit operating systems only.
For the next release of OCS, Microsoft will support deployments on 64 bit operating systems - Windows Server 2003 x64 (R2) and Windows Server 2008 x64.
They based their decision to go 100% 64-bit in part based on customer feedback, as they explained here:
Based on customer feedback, Microsoft's goal with the next release of OCS is to simplify deployments by reducing the number of servers needed for deployment. Customers are also telling us they are pushing the limits of existing hardware with their "mission critical" communications solutions.
OCS 2007 Video Call
There was a bit of a backlash from customers when Microsoft announced that Exchange Server 2007 would be 64-bit only, but I think that mentality has eased a bit over the last year. More IT departments are deploying 64-bit servers these days, so it's much less of an issue. Plus, OCS 2007 servers are installed by companies that are on the leading-edge of technology. After all, OCS 2007 is only 1-2 years old. Plus like Microsoft says, when you consider that enterprise communications are mission critical, why would stick with 32-bit when 64-bit works much more reliably?
I'm sure there will be those that disagree, but I for one am happy Microsoft is jumping in with both feet into the 64-bit world.