I would avoid Vista - it's crap.
However, I would go for XP on anything low powered like these EEE laptops. Virtualising the CPU and running windoze is just going to make it run even slower.
Also while pure browsing can be done on "anything", typical flight planning software is all windoze: Navbox, Jeppesen stuff, etc.
As regards free software, I thought most people already had that one sorted
(Don't get me wrong - I love M$ as much as everybody else, having just totally trashed my nice laptop with SP3)