Here's a look at the preliminary system requirements for Office 2013.
Perhaps one of the things that sticks out a little bit is that Windows XP and Windows Vista are no longer supported, users wishing to install Office 2013 need Windows 7, Windows 2008R2 or newer.
Preliminary system requirements for the Preview include the following:
Computer and processor: 1 Ghz or greater x86/x64 Processor with SSE2 instruction set
Memory: 1 GB RAM (32 Bit) /2 GB RAM (64 Bit)
Hard disk: 3.5 GB free disk space
Operating System: Windows 7 or newer, either 32-bit or 64-bit; Windows 2008R2 or newer with .Net 3.5 or greater. It isn’t possible to install on a PC running Windows XP or Vista. To use with Windows 8 you must be running the Release Preview version or higher.
Graphics: Graphics hardware acceleration requires DirectX10 graphics card and 1024 x 576 resolution