Many thanks for your prompt reply and help 747simpilot.
I read the thread you directed me too, and followed some of the advice given.
A boot scan with Avast! didn't turn up anything. Interestingly when I looked at the log file for the scan it said "scanning aborted" - this wasn't the case as I let it do it's thing then start up normally (took a little over an hour to complete)
I opened to host file in System32/drivers/etc as a text file - it had the 127.0.0.1 localhost line but also another line underneath it with just a few 0's.
Should I delete the line under the 127.0.0.1 one?