I'm having a similar problem, everytime I launch reader or if I try to open a PDF it crashes on my winxp sp3 PC with a visual c++ runtime error and closes. I can't even get to any preferences or anything in time.
My guess would be if you disable Protected Mode you will be ok. Try apply a registry file with the following:
Windows Registry Editor Version 5.00
Have/has the same issue. Disabling the protection didn't help so I made a deep deinstall of Reader X and reinstalled it and it worked again. So far so good.
I also noticed that the Adobe plug-in in Firefox (3.6.13) didn't work either. After reinstallation it worked again as well. I'll keep an eye on on it.
I work on a Windows SP3 machine.