I'm a great believer in that if you want to really do something then do it, but making windows has changed a lot over recent years and unfortunately the bureaucrats have got their stranglehold on the industry now.
I've been making doors & windows for well over 30yrs and if you'd posted say 5 years ago I would have replied and told you to forget it................... but the last 5 years have been good, timber windows are making a comeback for various reasons (I'll not go into them in this thread).
The market these days is for high quality, high performance windows and conservation replacement.
But the days of making any old windows & fitting them and walking away are long gone. You have to register them, pay your fees, get them approved pay more fees............it goes on & on. Make a small mistake with construction or design and you fall foul of building control & Fensa etc and it costs you even more. This year 2010 the rules change again making it harder for small firms to manufacture windows.
FWIW 40K is way to much to be spending on machinery imho especially to start out, I'd halve that.
As I said at the beginning if you really want to do it then do it and good luck, you never know until you try. But don't just make windows, be flexible and make just about anything.