Ill try and sort it out for ya, basically the "E" versions have been scrapped as M$ decided to bundle internet explorer with it again, currently their are 3 versions availble for mainstream use in england :
Windows 7 Home Premium
Windows 7 Professional
Windows 7 Ultimate
Their are "N" versions but i won't get in to them.
All 3 versions at this moment in time are full retail copys, this means you can install them on a PC without any other version of windows present, you can't install any of the 3 above versions over the RC candidate as they required a "fresh" install, this means a backup of your data and a wipe of the HD then install.
Home premium should be fine for basic gaming + office use, it doesn't include XP mode and has a memory cap of 16gb, personally i have 2 copys of Home Premium on order as i don't require the features of professional or ultimate but thats a choice you will have to make.
Currently Tesco are offering the pre order of Home Premium for £50
http://direct.tesco.com/q/R.206-3928.aspx