This video shows you how to install ATI driver on Linux Kubuntu 8.04 and how to setup Compiz effects. I would advise you to export your Compiz settings to file, because another setup will take many time.
Acer Aspire 6930G-644G32MI:
Intel Core2Duo T6400 2.0 GHz
4 Gb RAM
ATI Radeon HD4650 1 Gb
Intel WiFi Link 5100
Installed Debian and Compiz on to my Acer Aspire One laptop (the 1gb ram and 120gb HD version)
The guide how to manage this http://wiki.debian.org/DebianAcerOne