Upgraded a few different OSs to 4.8.1227.
Celeron M 2.0 GHZ, 2GB RAM,
Vista Home Basic - avast! Home, All Providers, No problems reported.
AthlonXP 2600+, 1GB RAM,
98SE - avast! Pro, All Providers, No problems.
AthlonXP 3000+, 768MB RAM,
95OSR2 - avast! Home, Standard Shield & Internet Mail only, No problems (didn't really expect any).