[villagetinker]

Aluminum is typically oxidized to form a very hard weather resistant coating. While this is quite good, it will eventually wear down to natural aluminum, which will tend to corrode. The above process is a chemical process, that as far as I know cannot be done at the house. There may be an option to paint the windows, but I have never had good luck with this.
My suggestion would be to get an estimate for replacement of the old aluminum windows with new windows (vinyl, aluminum, or wood) and then negotiate a revised price on the house. IMHO I would go for high quality vinyl (or vinyl over wood) double pane replacement windows. Also, depending on how handy you are this could be a do it yourself project.
Hope this helps.