Statement from Microsoft:
http://blogs.msdn.com/b/sharepoint/archive/2009/05/07/announcing-sharepoint-server-2010-preliminary-system-requirements.aspx
Q: Why are you only supporting the 64-bit versions of SQL Server 2005 or 2008 for SharePoint Server 2010?
A: This decision was based on our current test data for SharePoint Server 2010 and real world experience from customers running SharePoint Server 2007 with 32-bit SQL Server. SharePoint performance and scalability can benefit significantly from 64-bit SQL Server and the throughput increases are significant enough for us to make the difficult decision to only support SharePoint Server 2010 on 64-bit SQL Server 2005 or 2008. It has been our strong recommendation for some time that SharePoint Server 2007 customers take advantage of 64-bit SQL Server due to the inherent performance and scale benefits it can provide.
A scenario where you could run SP2010 with a 32-bit OS in play, is if you have a 32-bit OS installed on a 64-bit capable hardware (CPU, motherboard, etc). You could then install a 32-bit virtualization platform (like VMware Player, VirtualPC, etc) on the 32-bit host OS, but create a new virtual machine that is 64-bit, as the VM platform will take advantage of the 64-bit hardware.
You must make sure you have 64-bit capable hardware with virtualization technology (like Intel VT).
