Buy an RJ45 crossover cable for less than 5$, connect the laptops and you are all set. If your laptops are equipped with modern gigabit network cards a straight-through ethernet cable should work as well.
You should be able to uninstall vista (or xp or whatever) with the same CD that was used to install said operating system.For complete instruction visit: www.removevista.com
You can, but I would recommend using windows 7 rather than XP since some of the hardware may be incompatible with XP. Plus Windows 7 is pretty slick and fast, with much fewer problems than vista.