On a wheel designed to be a flip-flop wheel such as these: http://bikeisland.com/cgi-bin/BKTK_S...ls&ProdID=1533 the hub is spaced at 120mm with the fixed cog and the freehwheel being at the same spacing from the centerline of the hub. The wheels are not dished so they do not need to be re-dished or shimmed to be flipped around.

The wheels you posted apear to be road wheels which use wider hubs and can not (generally) be converted to run fixed. There is a kit that can convert those wheels to run [freewheeling] SS but buying wheels like that to run SS is like buying an airplane to get free peanuts; it'll work but there are better ways to do it.

If you are new to FG and wheels/wheelbuilding your best bet is to buy an off-the-shelf FG wheelset so you can learn how they work before trying to get too fancy building your own. The one listed above is $99 shipped and should be more than adequate to allow you to determine if FG is something you are interested in. You can always resell them later if you decide you want to upgrade to something nicer.