That sounds great.
My house, built in middle 80's still has the terrible original aluminum slider windows, with double pane glass, but very close together, not much air space gap.
I've been researching for a while, and need to get to this replacement project someday, too. I seem to be sort of set on Milgard brand from HD, and do the installation myself.
Could you please let us know what brand/style for your windows that you have chosen?
Please post pics when done for sure.
anyone have any comments about Milgard ?