Shabu is methamphetamine. It's street slang in (I think) Indonesia, but some part of southeast Asia or Polynesia anyway - maybe Fiji - where it is widely used. It's usually smoked as far as I know.
Due to immigration Shabu as a term is becoming more widely used in Australia nowadays, depending on the subculture you move in.
The street term "speed" in Oz refers to both amphetamine and methamphetamine, so you are quite correct in assuming that shabs means speed.
The term "Ice" in Australia usually refers to very pure recrystallised methamphetamine.
4-MAR is quite a different chemical with somewhat similar effects to methampetamine. In the USA 4-MAR is known as "Ice", although sometimes methamphetamine is called Ice there too. I don't believe that 4-MAR is available in Australia, at least not widely, but I'm open to correction.
In Erowid there are images of methampetamine crystals and 4-MAR. They look very similar indeed. The meth crystals tend to look like shards of clear glass (hence sometimes also known as "glass") while the 4-MAR shards are more opaque to white in colour.
[ 31 July 2002: Message edited by: D&AWg ]