Well, Honestly in Windows i dont think you can change the language like that. In linux it might, but i need to test it.
My Advice ?
Talk to a friend that understands a bit, and tell him about your problem. Tell him you want to dual boot. One OS for your Husband in spanish and another for ya in English. Its easy to do, quite fast to do aswell. You got your problem solved, and if one of your Windows just goes FUBAR (F*cked Up Beyond All Recognition) because of virus or just a bad update, you still have the other installation to salvage the data.
Much more i cant explain without entering in too much tecnical terms. Hope i helped.
If you are using XP open Control Panel and open Regional and Language Options. Click on the Language tab and work from there. You may have to load some language files from the Windows CD from there and activate the second language. Then, on the main task bar at the bottom of the Desktop, right click and there is a language bar to activate. You can switch between English and the language you have added. Not sure ths helps your situation, but this is how we use different languages for sending email and such.