I'm running Jaunty (9.04). the alt+tab effect looks very bad. Is there a way to change the alt+tab effect? maybe make it look more like a mac?
You want to install Compiz.
First enable proprietary drivers;
Go to System > Administration > Hardware Drivers, then click "Activate" for any drives provided.
You can then follow the Ubuntu.com compiz guide here.
Use ccsm (as shown in the guide) to change all manner of compiz settings, including the alt-tab decorator.