You can upgrade via a custom install. Look at the picture posted by dzadzev at the end it says: "In the EEA/EU Microsoft will ship..." etc.etc. This refers to N/E/K editions which lacks support of some programs like IE and WMP.
Why would you want to do this? N is only a slightly more crippled version of Windows. THere's really no point.
Only reason im gonna use it is because my MSDN gives me 10 keys for each version and felt like selling them to some not so close friends. Was curious about what upgrade path they could use. as I was going to have it install the WMP using the batch file.
Something I am curious about doing is replacing the pkeyconfig and what other files? To make the Ultimate accept UltimateN Keys.
It could be that Ultimate and Ultimate-N shares the same keys (it's the same edition, no sense to change the algorythm). I've installed on my PC a Home Premium (with its key) and then I've uninstalled Internet Explorer (I use Opera) and now in "System" it says Windows 7 Home Premium E and I haven't changed my key at all.
I tried activating a copy of mine using the N series Key and it didnt activate. Ill give VirtualPC a go in alittle bit.