Bonjour jupiterfrog,
I think the only thing in your hardware that could kill to this point Windows is the RAM, as rendering depends mostly on RAM and CPU.
256 Mb, with Windows 2000, is not that much. The system takes around 100 Mb, so it doesn't leave a lot. You should at least have 512... sorry to hear that you won't upgrade until you finish school. But I assure you it will make a difference.
In the meantime, you can turn on Verbosity in the Render Options (Logged Messages tab), and in the User Preferences, Scripting Logging tab, turn on Log Commands to File and Real-time Message logging. This will save to a file all that is logged in the Script Editor, so if your render crashes, you just to open this file and check what's the last thing XSI did. I might help you find if there is something in your scene that crashes the render.
Hope this helps
Salutations - Cheers
Bernard Lebel