Windows 7 Professional
What can I say.......Windows 7 is near enough perfection
This is what Vista should have been and was not. It will run on pretty much anything including small Atom powered netbooks. It is clean, simple and it does just work. The main bugbears of Vista ie annoying UAC, sluggish running and compatibility problems are banished, networking is easy as pie with the new Homegroups system (why has it taken so long for MSFT to install a simple way for ordinary folk to share their stuff securely?) Media Centre is excellent and very simple, overall it looks great - if strangely Mac-like ,,,,,,, however.....
My copy is a clean MSFT retail version System Builders (Dell, Acer, HP etc) insist on installing all the crapware they can possibly get paid to cram into their machines such as McAfee and Symantec rubbish and my pet hate of all time the Acer E Helper Toolbar which is a dreadful piece of unecessary crap, but as I just wipe and do a clean install minus the rubbishware.
Installation and Upgrading
Installation is best done as a clean install, trying to "upgrade" a machine is problematical it always has been. You can buy an "Upgrade Version" or a "Full Version" from Amazon for £64 & £99 respectively. Buy the upgrade version you can do a clean install with either even on a bare machine. The only criteria for using the "upgrade" version to do an install is that the machine must have Windows on it first (not activated even just there) so if you want to do an install on a bare machine all you have to do is install Windows 7 Upgrade twice ie over itself then you can activate it.
There are many versions but only 2 are important
Windows 7 Premium - this is the minimum version you should accept pre-installed for a home PC if you can get Windows 7 Professional then do so because.............
Windows 7 Pro is perfect for home and business, it has everything and most importantly it has "XP Mode" which will run your old XP applications especially important for businesses using old but mission critical applications.
Forget Windows 7 Ultimate it is a rip off, Windows 7 Business does have XP mode but not Windows Media Centre, Basic is rubbish and as for Starter Edition its for the third world to try and convince them a totally neutered operating system for 10 bucks is better than a full pirate version of Pro - good luck with that one MSFT.
64bit or 32bit? - Well I use both but in reality the 64 bit version is far more of a pain in the bum and most software does not have a 64 bit version - for a start I had endless trouble with i-tunes on the 64 version amongst other irritations and it is not noticably quicker than the 32 bit version on the same machine.There is a long standing technical arguement about 64 / 32 bit machine - the bottom line is that for high power intense stuff like "proper" video editing, 3D Modelling, CAD, Photo Editing and heavy duty number crunching 64 bit is the way to go. For the vast majority the tried, stable and well supported 32bit Windows is more than enough.
Well supported nowadays as 64 Bit becomes more common but you find most software except specialist professional photo / video editing is really still 32 Bit - that includes Microsoft Office 2010 and 2007.