Far too much work for that small amount of people to produce something binary compatible to WindosXP. The project started in the late 90s. Microsoft throw a bunch of people at all the security problems they have with their stuff, there is no way ReactOS ever could do even the same results, not expecting better results.

Get simply @thedead1440's advice, using the head start on Linux your N900 gave you! There are very fine communities around those Linux distributions, with great people sharing knowledge, giving support or just chatting away. Most of the installs use a fraction of harddisk space you are wasting on Windows system install space. Most of them offer full desktop software right with initial install, like Office software, email, browser(s), communication, image manipulation, lots of simple fun games and so on.

You could even have lots of Windows software run in virtual machine or wine (API compatibility layer capable of running Windows applications). In fact; Windows in Virtualbox is the only way i get my Audible audiobooks to my N900.