That depends on a whole lot of things! This will be available as a free upgrade to Windows 8 (as it is just a service pack with one or two features normally found in a new OS), if you are really unsure it would be best to wait. If you do decide to do it now, you have to choose the correct language version, the correct architecture (most should be using x64 now), the correct licensing system (VL / Retail etc), and of course, there is no guarantees that you can actually safely have it activated yet. I'm not saying that it can't be activated, just there's no guarantee that it will 'stick'.
preparing Finnish, Croatian, Chinese-Hong Kong SAR and Polish, all x64 files might be up tomorrow and running
don't know where you look but all my uploads are x64 only at this moment (few exceptions to be honest) .... might change later
they will be available when copo made magnets and announces these edit: we are only humans and do this here just for fun !!
links are either announced by ms-7 or copo in this thread. Page 1 is a good start I don't provide any links, I only get the material