For most gensets, simply changing the orifice and a few adjustments will allow the conversion.
Here are links with instructios and video:
http://www.thegoodsurvivalist.com/how-to-convert-your-generat ... read more
It depends on the type of window. Is it just a glass replacement or does really need the entire sash? Sometimes, the I.G. unit can be replaced using the same frame.