Being from the UK, garyrxl, your terminology is different than what is typically used in the US. The overall frame that holds the glass is called a sash. The dividers in the sash for individual panes of glass are called muntins. There are many ways to make these from ordinary hand tools to specialized cutters for routers or shapers. When you say twinsets, you are likely referring to these type of cutters. There are similar cutters for building cabinet doors which we call stile and rail sets or cope and bead sets. These are not quite the same as window muntin or sash cutters. Some of the cope and bead sets can be altered for glass but these are primarily for cabinet doors with a glass panel, not exterior house windows. For exterior window sash, you need a more substantial mortice and tenon. The "twinsets" only make a stub tenon.
http://www.finewoodworking.com/item/4790/making-a-window-sash-or-breakfront-cabinet-door
http://www.finewoodworking.com/item/4790/making-a-window-sash-or-breakfront-cabinet-door
