the 770 is already considered legacy, so there are no official software updates rolling out. So if you go for this Tablet now, you end up with - in NiT terms - outdated Hardware & Software.

The both N Series devices N800 & N810 are hardware wise pretty much the same (processing power) and most important those have the current OS2008 and a good perspective in the future mer project.

So go with N800 (you should get a used device for under 100 €), forget about the 770.