Installing programs on VISTA

Hello folks, I trying to install non-microsoft programs on my Vista
Business. Some of them are ok, but with TexNic, Notepad++, OpenOffice,
Thunderbird I am having problems.

Which problems?

Cannot copy EXE or DLL files into the target installation path:
c:\Program Files\XXXX

Could not write value for the key \Software\Classes\XXX

Could not write DLL files in the c:\windows\system32 path

Could not execute 7-zip

All the installation programs I am running with the "Run as
Administrator" option. All are with the compatibility mode
"Windows XP" and the privileges for administrators.

So, I cannot install these programs. Please I had a lot of
work delayed beacuse that, Could you VISTA gurus help me?
Is there some of you using MSN Messegner to help me?

Best regards,

Marco