I did that, after the computer rebooted Adobe took over again. I have windows XP. I never had an option to turn off updates from any menu using the free reader.
Well, on my system stopping Adobe's startup in msconfig stopped it for good, so you may have something else affecting it. You could always get Autoruns from SysInternals which gives you a lot more control over startups. As far as the option to turn off updates in Adobe Reader 8 (free) it is there. As I said in my other post you must go through these steps to get to it:
click - help>check for updates>preferences>then uncheck "Automatically check for Adobe updates"
One thing I did forget to mention last time though is that after clicking "check for updates" you must allow it to finish checking for new updates before it will give you the "preferences" option which is where you must go to turn off auto updates.
If you have swithced to either Foxit or PDF-Xchange viewer though you are better off anyway. I only use Adobe Reader on one system due to some files my daughter requires for school which will not work in Foxit or PDF-Xchange for some reason.