Vista - No internet connection when running antivirus?

I have a broadband wire connection with Virgin Media, their free antivirus (PC Guard) does not work with Vista 64 yet, so ive tries several others:
AVG free, downloaded and works fine, but cant connect to the internet
McAfee I cant complete the installation becuase it fails to connect
Avast downloads and works fine but again no connection,
each time I have to download them then the inetnet wokrs fine,
I have done a clean up to make sure there aren't any left over antivirus files that would conflict with each other but this hasnt worked either, I've been using CCleaner to do this
I have made sure that the windows firewall allows the programs access via exceptions, I've also tried with windows firewall off
I've only had the computer three weeks, it came with a free Bullguard trial, whihc ran fine, but it just seem to dissapear after only a week, I tried re-installing it but it wouldnt let me.
What else can I try???
Please help,
Colin.