Replace Timber Windows - Heritage overlay

Hi All,
Very new to this so not quite sure what is required from a 'best solution' perspective or from what is required due to heritage overlay.

Interested in replacing existing windows in 1930's house due to thermal and noise factors. Here are some photo's of the windows. (about 1.4m x.9m size)
http://imgur.com/a/Luaeg

Thoughts on what should be used for replacing them would be appreciated.
(I believe i am going to have to go with Timber - which i'm ok with as it goes with the style of house).

Will i need to replace the window frame? Any ideas on costs?

Thanks

Talk to the council as these windows can be repleced with aluminium which will look at least as good, and nobody would know they are aluminium unless they tapped them.Price around $1200 each installed complete... that is a guess.

Suitable brands would be those with an inline reveal, as they are a direct replacement for timber.

Ed