I would say... If you don't have any equipment yet and don't know how to use Cubase VST or cakewalk or if you are not too much into computers, go for an AKAI MPC2000XL or a Yamaha RM1X, or an equivalent... These machines are good realtime "instant action" devices, where you can sample, sequence, and add effects.

I know in Bjork's concerts, the guy has an AKAI MPC2000 or 3000 and a few other racks hooked to a digital mixer, and he performs almost all the music except the orchestral parts.

I assume those realtime machines can be controlled from a sequencer on a computer if later on you are getting a lot of new equipment and want to make the computer the center of your studio. As I said, one of those realtime action samplers/workstations would be a good choice to start your studio if you are focused on hiphop, triphop, and most other genres of electronic music.

As for portishead, massive attack etc.. The music you listen to has been recorded in Studio, mostly using ProTOOLs (digidesign) soft+hardware systems, where synthesizers, samplers, and turntable were recorded as audio sources. I am not sure what these people perform with when they play live though. They probably use samplers a lot, turntable in realtime, and they often plug everything to a hardware sequencer (such as the one on the MPC2000 for example) or I sometime saw laptop computers with an external MIDI interface (like the MIDIMAN USB Sport 8x8) to send the MIDI controls. It can be done with several different configurations.

Take care