No, you can't make LSD from Foster's beer. This myth started as a joke on the net and has spread far and wide. There are more than one official looking web site out there which describes in detail a respectable sounding extraction method. The main thing that should tell you there is no truth to this myth is that ergot is poisonous.
People die from ergot poisoning.
However, there is no ergot in Foster's Beer. There is nothing special about Foster's beer which would make it more likely to contain ergot than any other beer. According to Foster's web site, they brew a 'bottom fermented lager'. This is an extremely common beer to make and it's made out of rye, just like most other beers. The process of LSD synthesis is a complex one which requires a fully equipped laboratory.