turbocharger and supercharger

[blue00gt]

Yes, you can have a turbo and a supercharger both on the same motor - there was a rally car that had this configuration (I believe it was some kind of Lancia). You also need a very built motor with some careful tuning in order to handle that kind of a setup.
Twin turbo just means that there are two turbos. Many motors with two cylinder banks (V6, V8, etc.) have a turbo on each exhaust manifold. They also make sequential twin turbos, which are inline with each other and usually one is smaller than the other so that it spools up faster and reduces the amount of time it takes to start making boost. Big single turbos usually make alot more top end than a sequential setup, but also are usually less streetable because of lack of low end due to low compression to safely run high boost levels and the time it takes to spool up a bigger turbo.