Does it stop with an error message? If there is an error message it'll probably be easier to troubleshoot.
I see that you've tried firewall etc. But I wonder if this is still a permission issues.
- Are you logged on as an administrator? (You probably are, as you did manage to install Acrobat trial, but no harm in double checking)
- I'm wondering is Window's UAC is denying acess. See http://windows.microsoft.com/en-us/windows-vista/Turn-User-Account-Control-on-or-off and give it a spin
- An anti-virus is preventing installation. Turn-off anti virus for a while and try.
Thats all I can think of right now. let us know if any of these help.