Today the SharePoint team announced that SQL Server will be a prerequisite for SharePoint 2010. It was also announced that SharePoint will only come in the 64-bit version. So that means 64-bit SQL (2005 or 2008) and 64-bit SharePoint. Also SharePoint will require Windows Server 2008 or Windows Server 2008 R2, which only comes in a 64-bit versions.
This announcement is well ahead of the availability of SharePoint to give you time to prepare. Most medium to large scale SharePoint deployments are already running on this 64-bit configuration today with SharePoint 2007, as it is the current best practice. You should also use the SharePoint 2010 Upgrade Checker that shipped recently as part of SharePoint SP2. The upgrade checker will help you identify potential upgrade issues and blockers.
The last part of the announcement was around the set of supported browsers. IE 6.0 will no longer be supported with SharePoint 2010. Again you have some time to prepare if you company is still using IE6.
To recap the SharePoint 2010 announcement:
Arpan’s blog has a couple of good links to running and migrating to a 64 bit SharePoint 2007 environment.