trausti, sometimes 'stupid' questions can make someone approach the solution in a different way. Your questions aren't as stupid as you thought because in thinking about them, I too have learned something...
I will paraphrase the questions and try to give meaningful replies
1 Which templates can I use for TViX 66xx/N1?
Configure TViXiE for your player | Tools | Options | General | Model | select TViX M-6600-N
now click View Model details...
You will see
Model Name : TViX M-6600N
Background Filename : tvix.jpg
Background Width : 1280
Background Height : 720
Folder Filename : folder.jpg
Folder Width : 147
Folder Height : 200
However, I also know that people are using 1080p templates with these machines to get greater clarity. To do so, they will use a workaround to make the setup create the larger tvix.jpg.
So the answer is that you can use either 720p or 1080p templates (just make sure that the template is set to create a tvix.jpg and not for example a background.jpg
2 if i move the media center sometimes to a friends house which doesnt have hdtv, would 720p be a safer bet to work at both places
Both templates are basically the same apart from the fact that 1080p is obviously an enlared version of the 720p one. Whichever you choose to use would primarily depend on your own personal needs because when you go to a friend's house (who has only a SD format TV), you would configure TViX itself to output to a non-HDTV setting. The detail in the picture should really make no difference because under these circumstances, it would be TViX that would be downscaling pictures and video.
One thing that I became aware of after the release of the initial PEGGIE templates was the fact that a lot of people are still not able to cope with a full 720p image. Instead of seeing the background image fully, they notice cropping (especially at Left and Right edges). In the next versions of PEGGIE you will see that important information is moved more to the centre allowing more people to be able to use the templates without any noticeble loss of information.
I hope this helps