1. Essentially if you can't remember it you have o reinstall.
2. First you have to be strict in what starts on boot, many programs and their friends want you to to start them on boot by default. Only essential applications should be allowed to start on boot.
You can delay the avast update check, though you have to modify the avast5.ini file.
Using notepad (essential) open this file C:\Documents and Settings\All Users\Application Data\Avast Software\Avast\avast5.ini (XP location) Or C:\ProgramData\Avast Software\Avast\avast5.ini (Vista, win7). Locate the [InetWD] section heading and add the following line if it doesn't exist, AlwaysConnectedWaitSeconds=180 and place it after the AssumeAlwaysConnected=1 line (create if not present). Once you have completed the modification, save the changes, the avast self-defence module will ask confirmation about the modification, answer Yes.
See example below, which is for 180 seconds, you can increase that if required (another minute or two), but that should be fine.
[InetWD]
AssumeAlwaysConnected=1
AlwaysConnectedWaitSeconds=180