Are there any ad networks I can sign up for which allow me to put ads into a windows application? I am thinking of having both a paid version with no ads and a free version with ads of a software program.
Why not just place the ads on a real website, but embed an HTMLView, etc into app which displays your site?
Maybe you will be able to get in contact with some advertisers. Something like a sponsorship. They pay you and your software product promote them.