ERROR 123 FILE NAME SYNTAX

Hello,

I will explain my problem: when I try to install a software, after accepting the agreement and clicking next, here's what is written:
the installation wizard could not create the folder
''c\windows\system32\00:''.
error 123: syntax of the file name, volume name, or directory is incorrect.

I have seen other forums regarding error 123, but it’s not exactly the same error, which is why I took the liberty of creating a new discussion..

How did this happen? I was browsing the Internet, I was doing the co* (yes, it happens to everyone lol), and then my Avast started panicking: trojan, and it couldn't delete it. I immediately quit the Internet and disabled my Wi-Fi, I rebooted, ran a full scan, and neutralized the trojan. The problem is that it affected a file in the system 32, and I still deleted it... anyway. Since then my PC works fine except when it comes to installing certain software... I'm attaching a screenshot of what appears when I try to install it.. http://img837.imageshack.us/img837/5557/problemco.jpg

After searching online on forums about how it works, for example, they talk about a firewall, I disabled it, installed, disabled my antivirus during, and it still gives me the same message...
So maybe I'm wrong, but here I am an administrator of the PC with 2 sessions, but when I try to access certain folders, it tells me that I am not admin and I have to right-click to run as admin, etc... and for example, a strange thing, I cannot access the folders: Skype, iPod, and TuneUp Utilities 2010... strange... maybe the problem comes from there?? So, if a god can help me, I would be delighted!!!!
Thank you for your quick response.
Miky
Configuration: Windows Vista / Firefox 4.0.1