Minimum CPU and RAM requirements are unchanged from Office 2007, but the footprint of most Office applications have gotten larger. Most standalone application disk-space requirements have gone up by 0.5 GB and the suites have increased by 1.0 or 1.5 GB.
So in short, if your PC can run Office 2007, it will be able to run Office 2010. If you just acquired a brand new PC, it also will be able to run the forthcoming suite. But if you’re using Office 2003, there are no guarantees you’ll automatically be able to run Office 2010 on the same hardware.
The 32-bit version of Office 2010 will run on the following 32-bit operating systems: XP with Service Pack (SP)3, Vista SP1, Windows 7, Windows Server 2008 and Windows Server 2003 R2 (with MS XML). The 64-bit version will run on on 64-bit versions of all of these same operating systems, with the exception of Windows Server 2003 R2.
via Mary Jo Foley