If you OS is win9x or winME then the boot-time scan option will be greyed out (unavailable), the nearest you can come to a boot-time scan is by starting your system in safe mode (tap, tap, tapping the F8 key during boot), start avast and then run a full system scan in safe mode (where some malware, etc. won't be started.
We try to keep our avatars close to 100 X 100 for those with low resolution monitors or systems, you can use this one if you wish.
Welcome to the forums.
