I have vista, but when I put my clips into movie maker I have to convert them from a movie clip (amazing quality) too wmv. (kills the quality)but if you could also tell me how to get HD from movies too YouTube that'd be great 
alright
first of all, download a good converter
http://www.koyotesoft.com/indexEn.htmlthere u can download a converter called "Free Video Converter V2.9"
of course this one is for free
after u have downloaded and installed it, open it:P
tthen open ur file
on the left there is a list of output formats
choose wmv
then u can also choose the size
choose whatever u want, 720p, 1080 p or just keep the same quality (no change)
after u have converted it, just open windows movie maker and open the converted file
go on "publish to this computer"
later, there should be a list of 3 options:
"best quality for playback on my computer
compress to...
more settings"
choose more settings and then 720p or 1080p, whatever u want
we,,l i think that´s it and these steps make the quality of my videos clips even better
