Trojan mauled system, now can't reinstall Avast.

The other day, literally as I was updating my Java, a trojan jumped on my laptop. It was the Vista antispyware, one of many names I’ve come to find. I successfully? removed most of it, and it doesn’t show up on the system in the forefront anymore, but I’m thinking it has to be lurking somewhere, or has messed up a few things. The antivirus wouldn’t work on the computer, and it kept giving error messages, so I uninstalled it, cleaned the system and then tried to install Avast. Several attempts gives me this error message. I apologize if this incomplete information isn’t enough, but I just copied the errors setup log. I’m also a bit of an idiot so excuse me

18.12.2011 21:29:45 internet: SYNCER: Type: use IE settings
18.12.2011 21:29:45 internet: SYNCER: Auth: another authentication, use WinInet
18.12.2011 21:29:45 internet: Sending stats ‘http://download723.avast.com/cgi-bin/iavs4stats.cgi’: 00000000 204
18.12.2011 21:29:45 file: NeedReboot=false
18.12.2011 21:29:45 general: Return code: 0x00000005 [Access is denied.]
18.12.2011 21:29:45 general: Stopped: 18.12.2011, 21:29:45

Thanks in advance~

follow this guide and attach all logs…not copy and paste
http://forum.avast.com/index.php?topic=53253.0