Can I turn off my Windows Vista computer when it's updating?

I wanted to go to bed half an hour ago, and wondering why my computer hadn't turned off after about 5 minutes of being in bed, I checked it. Apparently it has a backlog of 18 updates and is installing them. Being a light sleeper, I can't sleep with my ancient PC whirring in the background. Can I turn it off? I'm going absolutely mad here.