After turning off the a/v scanner and redownloading the file I got further, but the Avast firewall will still not install properly. Here is an excerpt of the error log (see attached).
05.04.2011 16:02:25 system: Starting service aswNdis2
05.04.2011 16:02:25 system: Service aswNdis2 started, errcode: 0x00000000
05.04.2011 16:02:25 registry: Set registry: System\CurrentControlSet\Services\aswNdis\Parameters\ProgramFolder=\DosDevices\C:\Program Files\AVAST Software\Avast
05.04.2011 16:02:25 registry: Set registry: System\CurrentControlSet\Services\aswNdis\Parameters\DataFolder=\DosDevices\C:\Documents and Settings\All Users\Application Data\AVAST Software\Avast
05.04.2011 16:02:41 system: Couldn't copy aswNdisMp.inf, returned 0x80070005.
05.04.2011 16:02:42 system: NetCfgApi:InstallSpecifiedComponent returned 80070005
05.04.2011 16:02:42 system: aswNdis InstallSpecifiedComponent returned 0x80070005
05.04.2011 16:02:42 system: Couldn't install the network component, returned 0x80070005.
Other thoughts:
Although I don't have any other anti-virus/anti-malware software installed, I do have Blue Coat K9 Web Protection 4.0.296 and Secunia PSI 2.0.0.3001 installed. I'll try removing them to see if that helps.