Fraxinus, I omitted to mention that he is running Vista with OOo. He refuses to pay M$ for M$ Word.
My OO experience is almost entirely with Linux, Riki. However, I'd be surprised if the Windows versions behaved much different (although I know that many Linux distros, like ours, now package Novell's Go OO, which differs in some respects from the 'vanilla' versions from Sun).
My current install (3.1 from the repo here) seems to open .docx files fine - actually 2.4 did so as well.
The problem many of us have with opening docs created in Word 2007 is that Microsoft's default font for that version, Calibri, is not
freely available to people who do not have Office 2007 apps. Therefore, those not using Word 2007 can struggle to get docs to appear in the way that they did to their creators. (Surely this is by design on MS's part - they want to 'encourage' users either to use Word 2007 or to shell out money for their shiny new font.)
If this is a problem, and if you have a Windows box or VM, you can get hold of Calibri and hack it onto your system by downloading MS's free PowerPoint viewer for Windows - Google will offer detailed instructions. I have not done this, however. Instead, I am trying to encourage my collaborators to use other fonts and avoid getting sucked into Microsoft's nasty plan.